Introduction
Zambia’s growing urban areas face several mobility issues. Lusaka, the capital city of Zambia, has an urban population of over 2.5 million, with an urban growth rate of 4.9%. Rapid urbanisation, population growth, and motorisation are major issues to be considered in Lusaka to develop a sustainable transport sector. In Lusaka, 65% walk to their destinations, 23% use minibuses or taxis, 10% use private vehicles, and only 2% use bicycles. The data from this survey highlight the accessibility issues faced by residents, as well as important opportunities for sustainable change if the public transport system is electrified. Zambia does not have a specific strategy for electrifying transport. The 2019 National Transport Policy and the Eighth National Development Plan (2017-2021) have no sections dealing with the adoption of electric vehicles or charging infrastructure. On the other hand, the energy sector in Zambia is being restructured. A target of 1,000 megawatts (MW) of solar power generation capacity by 2025 is part of the country’s aim to reduce its vulnerability to climate change due to its over-dependence on hydropower. Transport electrification and renewable energy growth have the potential to result in sector coupling, in which the integration of mobility, buildings, and energy can yield beneficial systems that improve urban areas.

Methods
The study utilized policy landscape analysis, techno-economic evaluation, and comparative case studies. Through policy analysis, we reviewed Zambia's National Transport Policy, National Energy Policy, the Eighth National Development Plan, and urban development strategies for Lusaka and other cities to identify regulatory drivers and barriers for e-mobility. The techno-economic analysis compared costs of electric vehicles (EVs) and internal combustion engine (ICE) vehicles for applications such as public transport buses and passenger cars, using data on electricity rates, fuel costs, and incentives. Comparative case studies examined electric bus initiatives from African nations, including Kenya's BRT system and South Africa's electric minibus pilots, to identify applicable lessons for Zambia. Sector coupling was explored through scenario modelling involving vehicle-to-grid technologies and solar-powered charging stations. Stakeholder interviews with members of the Zambian Electric Mobility and Innovation Alliance, government entities, utilities, and transport operators provided insights into priorities and challenges in the e-mobility landscape.

Results
The present assessment has identified Zambia's specificities and barriers in deploying electric mobility. Policy instruments already implemented by the Zambian government have proven effective: the removal of import duties on EVs increased the number of registered electric vehicles by more than 300% in two years. The inclusion of Zambia in regional EV value chains, such as the tripartite agreement signed by Morocco, DR Congo, and Zambia, represents a means of localising content and stimulating technology transfers. A Total Cost of Ownership analysis shows that EV buses can be economically competitive with diesel buses in Zambia: the lifetime operational cost savings from electrification offset the higher capital cost. Sector coupling with Zambia's power sector, where solar PV deployment is on the rise and electricity networks are still developing, shows major potential for EVs in Zambia, which could help them serve as distributed energy storage units. Among the elements that could hold back further scale-up of electric mobility in Zambia are infrastructure-related factors. The charging infrastructure is still embryonic. The number of public charging points is low, and they are mainly located in Lusaka. The analysis of the barriers to the ZAMBIAeMOBILIZE project also identified barriers related to access to finance, a lack of technical capacity for charging infrastructure maintenance or installation, and a lack of grid connection capacity at locations where charging stations could be installed. Non-motorised transport requires better infrastructure and integrated action to close the missing link between homes and the electrified public transport systems. The NMT Strategy was adopted in 2019, but no further action has been taken to support its deployment, mainly due to a low investment in this mode and a lack of enforcement of the NMT standards.

Conclusions
Electrification of transport is a priority in urban areas where, when combined with integrated land use, urban transport, energy, and building sector planning, it can help Zambia achieve multiple development objectives, including increased mobility, better air quality, climate change mitigation, and a resilient energy sector. Zambia can move towards e-mobility by i) developing and updating transport and other related policies to mainstream electric mobility and EV charging; ii) leveraging concessional finance to procure electric buses and charging infrastructure; iii) enhancing technical skills to maintain the vehicles and manage the grid; iv) planning and investing in non-motorised transport to ensure last mile connectivity for users; and v) electrifying public transport that is used on high-frequency routes in Lusaka. Zambia could prioritise installing EV charging infrastructure at existing or new solar power stations and pilot vehicle-to-grid services. Zambia's rich critical minerals for battery production and value chain linkages with its neighbours can enable the country to tap into electric mobility markets.

Urban energy infrastructures are increasingly called upon to play a dual role: ensuring energy efficiency while simultaneously supporting environmental monitoring, climate adaptation, and inclusive governance. However, most smart city implementations continue to treat public lighting systems as isolated technological upgrades, rather than as systemic infrastructures capable of enabling participatory environmental intelligence. This paper addresses this gap by proposing a novel cybernetic framing of smart public lighting as a strategic AIoT-enabled infrastructure for environmental and climate justice within smart cities. The study responds to the need for integrated, scalable, and governance-oriented approaches that connect energy efficiency, environmental risk management, and open data-driven participation in the context of sustainable urban transitions.

The proposed approach introduces an AIoT-based cybernetic framework grounded in the Viable System Model (VSM) to reconceptualize smart public lighting networks as viable socio-technical systems. Methodologically, the framework integrates distributed environmental sensing embedded in public lighting infrastructure with AIoT data pipelines, edge–cloud processing, and open data platforms. The VSM is employed as an organizing meta-framework to structure system viability across five functional domains: System 1 (operational environmental sensing and energy-efficient lighting control), System 2 (coordination and data harmonization across distributed nodes), System 3 (operational control, performance monitoring, and resource optimization), System 4 (environmental intelligence, risk anticipation, and adaptive planning), and System 5 (policy, governance, and alignment with environmental justice objectives). This cybernetic architecture enables continuous feedback loops between energy infrastructure performance, environmental data production, and participatory governance mechanisms, operationalizing open science principles within urban management.

The results are presented at a conceptual and methodological level, demonstrating how the proposed framework advances beyond conventional smart lighting and urban monitoring paradigms. The framework articulates smart public lighting as a dual energy–environmental infrastructure capable of simultaneously improving energy efficiency, expanding high-resolution environmental monitoring, and enabling data-driven participation by local stakeholders. By embedding AIoT sensors within existing lighting assets, the model reduces marginal energy and infrastructure costs while increasing spatial coverage and temporal resolution of environmental data. The integration of open data and interoperable architectures supports transparency, accountability, and community engagement, transforming environmental monitoring from a purely technical function into a governance instrument. From a cybernetic perspective, the explicit mapping of VSM functions clarifies roles, feedback mechanisms, and decision pathways, strengthening system resilience and adaptive capacity in the face of environmental and climatic uncertainty.

The paper concludes that AIoT-driven smart public lighting, when designed as a cybernetic infrastructure, constitutes a powerful lever for smart cities seeking to align energy transition goals with environmental and climate justice. The proposed framework contributes theoretically by extending cybernetic governance models into the domain of urban energy infrastructure, and methodologically by offering a transferable blueprint for participatory, data-driven environmental management. As an initial case of application, the framework is contextualized through the Hub Ambiental del Caribe as an early methodological reference in the Caribbean region of Colombia, illustrating its relevance for cities facing environmental vulnerability and governance challenges. The approach provides a robust foundation for future empirical validation and positions smart public lighting networks as key enablers of sustainable, just, and resilient urban transitions.

Currently, the massive integration of electric vehicles (EVs) into the global mobility market has generated a growing and urgent need for the adequate planning, integration, and sizing of Electric Vehicle Charging Stations (EVCSs) within Distribution Systems (DSs). The primary objective of this integration is to maximize the available charging capacity while preserving the secure and reliable operation of the electrical network. However, the large-scale deployment of EVCS introduces a substantial increase in power demand, which can significantly affect grid performance. In particular, higher charging penetration levels intensify operational stresses on the distribution infrastructure, leading to potential violations of voltage regulation limits, thermal constraints of distribution lines, among others.

From a modeling perspective, the integration and sizing of EVCS constitute a highly complex optimization problem. This complexity arises from the nonlinear nature of power flow equations governing distribution systems, as well as from the coexistence of discrete decision variables, associated with the location of EVCS within electrical system, and continuous decision variables, related to their charging capacities. As a result, the problem is naturally formulated as a Mixed-Integer Nonlinear Programming (MINLP) problem, which is known to be computationally challenging, especially for large-scale networks and realistic operating scenarios.

To effectively address this challenge, it is essential to develop an accurate mathematical model that captures both the electrical behavior of the distribution system and the operational characteristics of EVCS. Moreover, the solution of such a model requires the use of high-efficiency optimization techniques capable of handling nonlinearity, mixed decision variables, and large solution spaces. In this context, this work proposes a comprehensive optimization framework for the integration and sizing of EVCS in distribution systems, with the objective of maximizing the total charging capacity while strictly satisfying all operational constraints of the DS under EVCS-intensive conditions.

As solution strategies, parallel implementations of Particle Swarm Optimization (PSO), a Population-based Continuous Genetic Algorithm (PGA), and Monte Carlo methods are employed. These methodologies are evaluated using a benchmark 33-bus distribution system, considering realistic variability in both photovoltaic (PV) generation and load demand. Each algorithm is executed 100 independent times to assess solution quality, robustness, repeatability, and computational efficiency, enabling a fair comparison and the identification of the most suitable approach for solving the proposed optimization problem.

Introduction

Urban service robots, such as last-meter delivery platforms, inspection robots, and indoor–outdoor logistics units, increasingly operate in cluttered environments where safe navigation must be balanced against limited onboard energy. In many deployed systems, path planning still prioritizes geometric shortest paths with collision penalties, which can produce stop–turn–go behaviors that increase battery drain and reduce operational endurance. This work proposes an energy-aware planning formulation for differential-drive robots in static polygonal environments, targeting smart city scenarios where repeated missions and charging constraints make energy a first-class criterion rather than an afterthought.

Methods

The workspace is modeled as a bounded planar set with obstacles represented by closed polygons. The robot footprint is modeled as a disk of radius with an additional safety clearance (c) , enforcing a minimum separation (r+c) from all obstacle boundaries. Candidate routes are parameterized as polylines connecting the start and goal through continuous intermediate waypoints, assembled into the decision vector x e R^2m .

Energy is modeled through a physically interpretable proxy consistent with differential-drive motion primitives: the robot rotates in place to align with the next segment and then translates along that segment. The objective combines translational effort, proportional to total route length, and rotational effort, proportional to cumulative heading changes and their concentration, capturing the fact that frequent or abrupt turns increase wheel actuation and dissipative losses.

Feasibility is enforced through exact geometric checks for polygonal obstacles. For each segment, collision and clearance are verified via segment–polygon intersection tests and minimum segment-to-polygon distance calculations, eliminating the false negatives that occur with coarse point sampling. Boundary constraints restrict intermediate waypoints to the admissible workspace, and an optional turning constraint bounds inter-segment heading changes to avoid extreme cornering demands. The optimization is solved using continuous metaheuristics, genetic algorithms and particle swarm optimization, with a feasibility-first constraint handling rule: any feasible solution dominates any infeasible solution, among feasible solutions lower energy dominates, and among infeasible solutions lower constraint violation dominates. This removes dependence on penalty weight tuning.

Results

In simulated urban-like layouts with multiple polygonal obstacles and narrow corridors, the feasibility-first energy formulation consistently produced collision-free routes that favored smoother steering sequences compared to distance-only planning and penalty-weighted feasibility schemes. The energy-aware objective reduced stop–turn–go patterns by discouraging sharp heading discontinuities, while the exact polygon distance evaluation improved reliability by preventing missed collisions between sampled points. Across repeated random initializations, both metaheuristics converged to feasible solutions when feasible corridors existed, with a genetic search showing strong exploration in cluttered maps and particle swarms showing rapid improvement in early iterations. The method also demonstrated stable behavior under changes in obstacle shape and arrangement, since feasibility is enforced by dominance rules rather than fragile penalty scaling.

Conclusion

An energy-aware, feasibility-first route planning method is presented for differential-drive robots navigating static polygonal environments, aligned with smart city service robotics where endurance and safety must be co-optimized. The combination of an interpretable energy proxy, exact polygonal clearance checks, and dominance-based constraint handling yields robust feasible trajectories without ad hoc penalty tuning. Future work will integrate platform-specific calibration of energy coefficients from measured power profiles and extend the formulation to time-parameterized control optimization while maintaining polygonal safety guarantees.

The paper examines how energy companies integrate social responsibility into the twin transition, defined as the simultaneous shift toward a low-carbon economy and deep digitalization, and argues that CSR must evolve from peripheral compliance to a core strategic imperative in this context. The study combines conceptual analysis with evidence from recent industry data on renewable energy expansion, digital investments (AI, IoT, smart grids, data analytics) and corporate ESG practices, highlighting how environmental, social and digital ethics intersect in corporate strategies. It explores four key dimensions: environmental stewardship beyond carbon (biodiversity, water, circular economy, waste reduction), community and stakeholder engagement, data privacy and cybersecurity for critical infrastructure, and innovative financing mechanisms (green bonds, sustainability funds, shared value models) that can support responsible transition pathways.

Methodologically, the paper advances a staged implementation framework that connects assessment, planning, implementation and evaluation in a continuous learning cycle, thereby making explicit the causal links between strategic intent, operational change and observed socio-environmental outcomes in the context of the twin green–digital transition. Within this framework, the assessment phase combines diagnostic tools on digital maturity, climate risk exposure and stakeholder expectations, while the planning phase translates these diagnostics into integrated portfolios of low-carbon and data-driven investments that are aligned with evolving ESG standards and regulatory trajectories. The analysis further systematizes typical implementation challenges into financial, institutional and socio-political categories, emphasizing how high transition costs, regulatory complexity and tensions between short-term shareholder value and long-term sustainability commitments interact to slow down or derail transformation processes. Empirically, the findings indicate that firms which embed social responsibility into the core of their governance architectures, risk management systems and digital innovation strategies develop more robust capabilities to secure and reproduce their social license to operate under tightening climate and digital regulation. In these firms, digital technologies are mobilized not only for efficiency gains, but also for enhanced transparency, participatory engagement and real-time monitoring of environmental and social impacts, which in turn supports higher levels of stakeholder trust and perceived corporate credibility. The paper proposes an integrated outlook in which environmental, social and digital ethics are treated as mutually reinforcing components of a unified governance paradigm for energy companies, rather than as separate or competing agendas. By adopting this unified normative basis, energy firms can reposition themselves as key enablers of a just and inclusive twin transition, leveraging their infrastructural, financial and data capabilities to support decarbonization, social protection and fair access to digital and energy services, especially for vulnerable groups.

The paper analyses the role of universities as key actors in the green transition ecosystem, focusing on the interface between smart cities, urban management and different stakeholders. From a multi-level governance perspective, universities are approached as nodes of knowledge, innovation and policy co-creation, capable of integrating the objectives of decarbonisation, urban resilience and digitalisation into local development strategies. The study examines three main dimensions: (1) the university as a provider of scientific expertise and data for smart urban planning; (2) the university as a facilitator of green innovation and technology transfer, through urban living labs, innovation hubs and public–private partnerships; and (3) the university as a normative and educational actor, forming green and digital competences for local administrations, businesses and citizens. In the cities included in the European mission "100 climate neutral cities", local universities provide expertise for energy transition plans, decarbonization scenario assessments and green mobility solutions. In addition, in Romania, universities participate in national platforms and initiatives such as "The Future of Energy", where industry experts and academics contribute to the debate and co-design of policies for the transition to renewable sources alongside the younger generation. Various universities in Romania are involved alongside energy companies in national and European projects aimed at deeply modernizing energy systems through advanced technologies and interdisciplinary solutions regarding smart grids, energy storage, energy-efficient buildings and the digitalization of energy systems. The methodology combines conceptual and policy analysis with case studies on university initiatives integrated into smart city strategies and local climate action plans. The results highlight that universities can function as orchestrators of the green transition ecosystem, accelerating the integration of digital and sustainable solutions in urban management, with direct impact on the quality of governance, community participation and environmental performance at the urban level. In this role, universities operate as intermediary institutions that connect local authorities, businesses, civil society and technology providers, facilitating dialogue, co-creation and experimentation around low-carbon, resource-efficient and data-driven urban solutions. By leveraging their research capacities, living labs and interdisciplinary expertise, they help translate climate and digital strategies into concrete pilot projects, decision-support tools and evidence-based policies that can be scaled across the city.

The assessment of Smart City performance has progressively evolved from competitive benchmarking-based assessment exercises toward evaluation models grounded in internationally recognized standards of sustainability, resilience, and governance. In Brazil, this evolution is clearly reflected in the methodological transition between the 2024 and 2025 editions of the Connected Smart Cities (CSC) Ranking, the country’s most comprehensive smart city intelligence ecosystem. This study examines this transition as a fundamental shift in the philosophy of urban assessment, moving from a logic of peer-based competitive comparison to one centered on adherence to international quality benchmarks. The objective is to analyze how this normative turn reshapes urban governance frameworks and management practices, with a particular emphasis on energy planning as a strategic dimension of smart and sustainable cities. The 2024 edition of the CSC Ranking was based on a weighted, comparative assessment grounded in the Market Quality Index (Índice de Qualidade Mercadológica, IQM). In this model, urban performance was assessed relative to the observed maximum and minimum values within the group of analyzed cities, comprising 656 municipalities with populations above 50,000 inhabitants. Indicators were assigned differentiated relevance weights ranging from 0.5 to 1.0, enabling the ranking framework to capture structural interdependencies among thematic axes while emphasizing competitiveness and relative positioning. Within this structure, the energy axis did not receive an independent ranking, as it comprised only four indicators mainly related to renewable energy sources and intelligent public lighting, resulting in limited analytical density and reduced applicability to strategic urban management. The 2025 edition introduces a paradigmatic methodological shift by adopting a normative, non-weighted, and universal assessment framework. The new CSC model expands its territorial scope to all 5,575 Brazilian municipalities and is explicitly grounded in ISO 37120 (urban services and quality of life), ISO 37122 (smart cities), ISO 37123 (resilient cities), and ISO 37125 (ESG indicators for cities). Rather than ranking cities based on relative performance, the 2025 framework assesses absolute performance by measuring each municipality's distance from predefined reference values or targets established by international benchmarks, such as those proposed by the United Nations (UN) and the World Health Organization (WHO). Methodologically, this shift entails adopting a simple arithmetic mean to calculate overall and thematic scores, assigning equal weight to all 75 indicators. This design choice aims to improve the transparency, communicability, and accessibility of results for a broad audience, including public managers, policymakers, and civil society. Scores are standardized on a 0–100 scale, with 100 representing full achievement of the reference value. As a result, the CSC 2025 framework primarily serves as a diagnostic and management-orientated assessment tool, focusing on progress toward global standards rather than on relative competition among municipalities.The implications of this transition for urban governance and management are substantial. First, the universal coverage of municipalities transforms the CSC framework into a nationwide monitoring instrument capable of revealing structural disparities across regions and city sizes. Second, alignment with ISO standards and the Sustainable Development Goals (SDGs) enhances international comparability and strengthens the credibility of urban data, potentially increasing cities’ attractiveness for investment and international cooperation. Third, integrating the MySmartCity platform enables continuous monitoring of indicators, supporting interdepartmental coordination and evidence-based decision-making. Finally, the distinction between ranking and certification becomes explicit: while the CSC provides comparative diagnostics, standards-based certification processes focus on verifying data quality and methodological conformity, allowing municipalities to evolve through certification levels without normative judgment of performance. Energy planning emerges as one of the most relevant dimensions affected by this methodological shift. In the 2025 framework, energy becomes a ranked thematic axis supported by ISO-based indicators that capture multiple facets of urban energy systems. These include decentralized energy generation, measured as the proportion of locally produced electricity relative to total consumption; energy efficiency, assessed by final energy consumption per capita; and electromobility infrastructure, evaluated by the availability of electric vehicle charging stations. This expanded treatment positions energy not merely as a technical subsystem but as a strategic component of integrated urban management, closely linked to climate resilience, mobility systems, environmental performance, and governance practices. Despite the move toward a more normative structure, the CSC 2025 model preserves the foundational principle of sectoral interdependence that characterized earlier editions. Urban development is understood as a holistic process in which improvements in one domain, such as energy or sanitation, generate cascading effects across health outcomes, economic productivity, and social well-being. This interconnected perspective is reinforced by consolidating related themes into broader thematic axes, fostering integrated policy analysis and coordinated urban management. Overall, the transition from CSC 2024 to CSC 2025 represents a significant maturation in the assessment of Brazilian cities, redirecting urban governance frameworks and management practices toward systematic alignment with internationally recognized sustainability and quality benchmarks.

IntroductionIn
In the face of rapid global urbanisation, the need for sustainable energy systems and infrastructure is becoming increasingly pressing. Cities now host over 50% of the global population and account for around 75% of primary energy consumption and 80% of anthropogenic greenhouse gas emissions. As urban energy demands continue to grow, conventional centralised grid infrastructure, with its one-way power flows and relatively inefficient energy transmission and distribution, is struggling to keep up with the evolving needs of cities and their inhabitants. Integrated urban energy systems, including smart grids, microgrids, and district-level energy optimisation systems, are emerging as a potential solution to these challenges, with their potential to enhance energy efficiency, flexibility, and resilience while simultaneously reducing environmental impact. Smart grids are electric power grids that utilise information and communication technologies to optimise electricity flow, facilitate two-way power flows, and provide grid stability and reliability, even in the presence of variable renewable energy sources. Microgrids, on the other hand, are localised energy systems that can operate in both grid-connected and islanded modes, integrating distributed energy resources, such as solar PV, energy storage, and controllable loads, to provide improved reliability and autonomy. At a larger scale, district-level energy optimisation involves coordinating energy systems and infrastructure at the neighbourhood level to enable energy management and optimisation across multiple buildings, transport systems, and infrastructure. This paper provides a detailed analysis of the various aspects of integrated urban energy systems, including their technologies, architectures, operations, challenges, and implementation strategies, with a focus on demand-side management, peer-to-peer energy trading, and the coordination of DERs in urban electric grids.

Methods
The paper uses a mixed-methods approach, integrating a systematic literature review with a comparative case-study analysis to provide a comprehensive overview of the state of the art in urban energy systems. The research comprises three key elements. First, a bibliometric review was conducted to identify peer-reviewed articles on smart grids, microgrids, and the optimisation of urban energy systems from 2018 to 2025. Second, a content analysis of the identified literature was conducted to map technological solutions and implementation strategies. This analysis categorises findings into five key thematic areas: (i) grid modernisation and smart grid technologies; (ii) microgrid and distributed energy resource (DER) integration; (iii) demand response and demand-side management (DSM); (iv) peer-to-peer (P2P) energy trading and local energy markets; and (v) district energy planning and positive energy districts (PEDs). Third, selected case studies of deployed urban energy systems were analysed to understand their performance metrics and operational insights, including the Brooklyn Microgrid pilot project, the Amsterdam Smart Grid program, and European Positive Energy District projects. The assessment framework combines quantitative measures such as energy efficiency gains, peak load shaving, and carbon emission reductions with qualitative evaluations of policy frameworks, stakeholder participation, and enabling regulations.

Results
A key finding from the literature is that, while significant technological progress has been made in integrated urban energy systems, several implementation barriers remain. The reliability and integration of renewable energy in smart grids have shown measurable improvement, and smart meters and other AMI technologies have provided real-time visibility into the urban electric grid. Energy resilience has also improved in microgrid systems, and it has been shown that optimal control of a group of microgrids can enhance the self-consumption of locally produced renewable energy. The benefits of peer-to-peer energy trading have been discussed, and the use of blockchain smart contracts to manage local energy sharing has been proposed to improve prosumers' energy balance within the urban energy system. Demand-side management strategies, including real-time pricing and incentive-based demand response, have been effective in flattening cities' load curves. District-level optimisation, particularly in the form of Positive Energy Districts aiming for net-zero energy districts, is a feasible strategy when high-efficiency buildings are combined with on-site renewable energy generation and advanced energy management systems. Some of the barriers identified include a lack of regulations aligned with the decentralised nature of smart energy systems, interoperability issues across diverse devices, cybersecurity risks, and social equity concerns.

Conclusions
Smart grids, microgrids, and district-level optimisation are three types of integrated urban energy systems that are crucial to the transition towards sustainable, climate-neutral cities. However, for these systems to be implemented at scale, several prerequisites must be met. These include advancements in technology, supportive policies and regulations, financial incentives, and stakeholder collaboration. In the near future, research should focus on the challenges and opportunities of integrated urban energy systems, including the scalability of successful pilot projects, standardisation of interoperability protocols, integration of artificial intelligence and machine learning for predictive energy management, and inclusive governance models to ensure equitable access to the benefits of these systems for all segments of urban populations.

Introduction

The transition toward sustainable energy systems and decarbonization has driven the development of energy conversion technologies integrated with renewable sources. In this context, solid oxide electrolysis cells (SOECs) are promising technologies for the electrochemical conversion of CO₂ and H₂O through co-electrolysis, producing synthesis gas and fuels from renewable electricity. Conventional electrodes, particularly Ni-YSZ anodes, suffer from degradation due to coking, sulfur poisoning, and loss of stability under variable operating conditions. Advanced mixed ionic–electronic conductors (MIECs), such as PBMO (PrBaMn₂O₅_+δ), LSCM (La₀.₇₅Sr₀.₂₅Cr₀.₅Mn₀.₅O₃_-δ), LSF (La₁₋ₓSrₓFeO₃_-δ), LSCF (La₁₋ₓSrₓFe₁₋ᵧCoᵧO₃_-δ), and LST (La₀.₂Sr₀.₈TiO₃_+δ) [1], exhibit robust structural stability and versatile functionality. Among them, double-layer perovskites such as PBMO stand out due to their high electrical conductivity, fast oxygen exchange kinetics, excellent redox tolerance, and stability against carbon and sulfur. In this way, symmetric solid oxide cells have emerged as an alternative, employing a single ceramic material as both electrodes, which simplifies fabrication processes, reduces costs, and improves material compatibility, while also enabling their application as reversible electrodes in SOFC/SOEC systems [2].

Materials and methods

In this work, different PBMO samples were synthesized via mechanosynthesis of binary oxides using high-energy planetary ball milling. Symmetrical cells with a PBMO–GDC / GDC / YSZ / GDC / PBMO–GDC configuration were fabricated using YSZ electrolytes prepared by the tape-casting technique. A protective GDC layer and the electrode layers were deposited by semi-automatic ultrasonic spray coating. The electrode powders, mixed with 50 wt.% GDC, were symmetrically deposited onto the YSZ electrolyte and subsequently sintered. The performance of PBMO electrodes was evaluated through electrochemical and microstructural characterization, considering their activity in electrolysis and H₂O/CO₂ co-electrolysis. Electrochemical measurements were carried out using an open-flanges test set-up, which allowed a rigorous assessment of the activity of the electrodes in reversible operation, both in fuel cell and electrolyzer modes. Durability and redox stability during operation cycles were also analyzed, correlating post-mortem microstructural changes with electrochemical performance. Microstructural characterization included electrode morphology by scanning and transmission electron microscopy (SEM/TEM), and elemental mapping by energy-dispersive X-ray spectroscopy (EDX).

Results

The results showed that in steam electrolysis mode (75% H₂O / 25% H₂), the cells exhibited a clear temperature-dependent behavior, with a decrease in operating voltage as the temperature increased from 800 to 900 °C at a given current density. Current densities above 250 mA cm⁻² were achieved at voltages below ~1.35 V at 900 °C. Electrochemical impedance spectroscopy (EIS) revealed a significant reduction in polarization resistance with increasing temperature, indicating enhanced electrode kinetics. Under co-electrolysis conditions (45% H₂O / 45% CO₂ / 10% H₂), similar trends were observed, with improved performance at higher temperatures and current–voltage characteristics comparable to those obtained under steam electrolysis. The EIS spectra showed a decrease in total resistance with temperature, confirming the positive effect of thermal activation on charge-transfer processes and surface reactions during co-electrolysis. Short-term constant-current tests conducted at 850 °C under 50% H₂O and a current of 800 mA showed a stable voltage response over time, indicating good operational stability of the PBMO–GDC electrodes under high current density conditions. Post-mortem characterization by scanning electron microscopy (SEM) revealed a dense and homogeneous microstructure, good interfacial adhesion between layers, and the absence of delamination or fracture after electrochemical operation.

Conclusions

Mechanochemical synthesis enabled the production of phase-pure PBMO materials with a uniform morphology and properties suitable for electrode processing and integration into electrochemical cells. PrBaMn₂O₅_+δ, employed simultaneously as both anode and cathode in symmetric SOECs, exhibited promising electrochemical performance under H₂O/CO₂ electrolysis and co-electrolysis conditions, with a clear enhancement in performance at higher operating temperatures. Symmetric cells with PBMO electrodes showed a homogeneous microstructure, adequate porosity, and excellent interfacial adhesion between layers, evidencing high structural integrity. In addition, constant-current tests confirmed the electrochemical operational stability of the PBMO-based symmetric configuration, with no signs of degradation observed during prolonged operation.

Acknowledgements

This work was carried out within the Renewable Energy and Hydrogen Program, included in the Complementary R&D&I Plans of the Spanish Ministry of Science, Innovation and Universities (MICIN), and was funded by the European Union's NextGenerationEU, under Component 17 of the Recovery, Transformation and Resilience Plan (C17.I01.P01).

It is also framed within the research project PID2024-162053OB-C31, funded by the Spanish Ministry of Science, Innovation and the State Research Agency (AEI), as well as the project SBPLY/24/180225/000095, funded by the Regional Government of Castilla-La Mancha (JCCM).

References

[1] Wang, M., Wang, J., Du, J., “A symmetrical solid oxide electrolysis cell supported by nanostructured electrodes for highly efficient CO2 electrolysis”, Journal of Power Sources 2024, 610, 234742.

[2] Garcia-Garcia, F.J., Sayagués, M.J., Gotor, et al., “A Novel, Simple and Highly Efficient Route to Obtain PrBaMn₂O_5+δ Double Perovskite: Mechanochemical Synthesis”, Nanomaterials 2021, 11, 380.

The large-scale deployment of green hydrogen technologies based on proton exchange membrane (PEM) electrolyzers and fuel cells is widely recognized as a key pillar for global decarbonization strategies. However, analyses conducted by organizations such as the International Renewable Energy Agency (IRENA) and the United States Department of Energy (DOE) consistently highlight that the economic viability and scalability of these technologies remain strongly constrained by their reliance on platinum group metals (PGMs) [1]. In particular, platinum loadings must be significantly reduced in both PEM electrolyzers and fuel cells to meet future cost targets. This challenge has stimulated growing interest in strategies that simultaneously minimize catalyst usage and enable the efficient recovery and recycling of critical raw materials from end-of-life components.

In this context, the present study addresses the recovery and reuse of platinum-based catalysts from exhausted PEM system components, with a specific focus on titanium porous transport layers (PTLs). We report the development of a novel, predominantly mechanical recovery procedure for Pt/C catalysts that enables the reuse of the entire catalytic ink, rather than isolated platinum. By avoiding chemically intensive processing steps and the use of expensive reagents, this approach offers a potentially more cost-effective and environmentally favorable alternative to conventional recycling pathways reported in the literature. The proposed method is systematically compared with established recovery techniques, including electrochemical dissolution of Pt from used electrodes and its subsequent catalyst synthesis, which typically involve higher process complexity and material costs [2].

Methods

Recovered Pt/C catalysts were reformulated into inks and redeposited onto several substrates via spray coating (airbrush Vega V2000). The electrochemical performance of the recycled catalysts was evaluated through a combination of several tests. The characterization included cyclic voltammetry to determine key parameters such as the specific electrochemical surface area (SECSA), providing insight into catalyst accessibility and utilization after recovery. Polarization curves and electrochemical impedance spectroscopy were used in PEM fuel cells to assess overall cell performance, kinetic behavior, and transport losses. In addition, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS) was employed to analyze catalyst morphology, dispersion, and elemental composition following recovery and redeposition.

Results and Conclusions

This study presents a novel approach for the recovery of Pt/C catalysts supported on titanium porous transport layers (PTLs), demonstrating its applicability in PEM fuel cell systems and enabling a direct comparison with established recovery protocols reported in the literature. The recovered catalytic ink, obtained directly from PEM electrolysis PTLs with recovery efficiencies of up to 95%, was successfully reused in PEM fuel cells. Although functional operation was achieved, the electrochemical performance did not fully meet initial expectations when compared with catalysts recovered using alternative methods, indicating that additional optimization of the recovery and reformulation processes is required. Furthermore, challenges were identified in the quantitative determination of the specific electrochemical surface area (SECSA) for catalyst layers deposited on carbon paper containing Pt/C and Nafion, highlighting limitations associated with substrate effects and measurement methodologies. Despite these challenges, the results confirm the technical feasibility of reusing mechanically recovered Pt/C catalysts and underscore the potential of simplified, cost-effective recycling routes as viable alternatives to more complex and resource-intensive recovery strategies.

References

[1] U.S. Department of Energy. Hydrogen and Fuel Cell Technologies Office Multi‑Year Program Plan (MYPP) 2024; Hydrogen and Fuel Cell Technologies Office, Office of Energy Efficiency & Renewable Energy: Washington, D.C. (2024).

[2] Montiel, M.A.; Granados-Fernández, R.; Díaz-Abad, S.; Sáez, C.; Fernández-Marchante, C.M.; Rodrigo, M.A. and Lobato, J. Towards a circular economy for Pt catalysts. Case study: Pt recovery from electrodes for hydrogen production. Applied Catalysis B: Environmental, Vol. 327, 122414, (2023).