Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are critical for the efficient functioning of fuel cells, electrolyzers, metal–air batteries, etc. It is well known that Pt-based catalysts are excellent for ORR but are poor for OER; similarly, Ru,Ir-based materials are excellent for OER but poor for ORR. However, these materials (Pt, Ir, Ru) are expensive and less abundant. Therefore, there is a need to develop cheaper and sustainable alternatives that are good at both ORR and OER (bifunctional) so that they can be used in regenerative fuel cells, which can operate as a fuel cell and water electrolyzer. Herein, we report a simple synthesis method for the formation of a NiO/Co₃O₄ composite, as confirmed by a multitude of characterization techniques, namely X-ray diffraction, Raman scattering, X-ray photoelectron spectroscopy (XPS), etc. The noble-metal-free composite, i.e., NiO/Co₃O₄ composite, was tested as a bifunctional catalyst for OER and ORR. The composite exhibited excellent performance in ORR and OER with very low catalyst loading. An onset potential of 0.73 V vs. RHE at 0.1 mA/cm² for ORR and an overpotential of 0.48 V vs. RHE at 10 mA/cm² for OER were obtained for the composite. The redox couples Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ and oxygen defects in the composite are attributed to the enhanced OER and ORR performances. These results are quite encouraging given that the synthesis of the composite is simple, and the precursors used for the same are environmentally benign.

In practical catalysis, it is often required to focus not only on catalyzing a desirable reaction but also inhibiting an undesirable reaction. Such is the case of the hydrogen anode in the proton-exchange membrane fuel cell (PEMFC), which is an attractive power source for long-distance trucks, where it has a weight advantage in comparison with battery power. The desirable reaction is the hydrogen oxidation reaction (HOR), but an undesirable reaction can also occur simultaneously, namely the production of hydrogen peroxide at the hydrogen anode from oxygen gas diffusing from the oxygen cathode. This hydrogen peroxide can attack the membrane, either directly or after it decomposes, to produce hydroxyl radicals in a Fenton reaction. This attack can severely limit the membrane's lifespan, thus increasing the operational cost. We recently found that a platinum alloy with cobalt was effective in inhibiting peroxide production, because the coverage of adsorbed hydrogen on the catalyst was smaller than that on pure platinum. In order to make further progress, it is necessary to carefully examine all of the possible reaction pathways involving various types of adsorbed hydrogen with O2, including bridging and on-top hydrogen on (111) facets, bridging hydrogen on (100) facets, and on-top hydrogen at (110) steps (V configuration) and (110) edges. Based on our recent density functional theory (DFT) calculations, the V configuration is particularly important, especially since it is also involved in the HOR itself, so we must be careful to preserve the high activity of this reaction while inhibiting peroxide production. We predict that pure Rh and Ir as well as PtRh and PtIr alloy catalysts will all be effective, since they adsorb less H overall at given potentials, require more negative potentials to adsorb H, and also adsorb O2 in a bridging configuration, making it unable to produce H2O2.

In a number of proton-exchange membrane (PEM) fuel cell applications, the storage and subsequent start-up under subzero temperatures is required. If water (the product of an electrochemical reaction) is frozen in the bipolar plate channels, gas diffusion electrodes, and membrane-electrode assemblies in a switched-off fuel cell at subzero temperatures, their destruction may occur as a result of an increase in the volume occupied by water when it is converted to ice by, ca., 9%. The original methods of PEM fuel cell conditioning before storage and subsequent start-up at subzero temperatures are suggested in this communication. In particular, the electrocatalytic self-heating of PEM fuel cells in the maximum power mode is proposed to increase its temperature up to 100-130 °C, which makes it possible to transfer water from a liquid to a gaseous phase, and effectively remove it by purging the internal cavities of the fuel cell with reagent gases (hydrogen, oxygen, or air). Corresponding strategies developed by the author and the engineering solutions realized in the experimental set-up are reported and discussed. It is shown that the suggested approaches for PEM fuel cell conditioning before it is shut down allows one to work out the issues of the storage, transportation, and cold start of PEM fuel cells at deeply negative temperatures. This work was supported by the Ministry of Science and Higher Education of RF under the project FSWF-2023-0014.

Introduction. Intermetallic compounds (IMCs), which have a homogeneous structure of active centers with controlled electronic structures and an atomic ensemble size, can be used to create catalysts with unsurpassed practical characteristics, including for demanding and stable electrochemical reactions such as nitrogen reduction (NRR), nitrate reduction (NO₃RR), and nitrite reduction (NO₂RR), which can serve as a replacement for the industrial Haber–Bosch process. An urgent task is to develop efficient electrocatalysts using cheap base metals, with partial or complete replacement of noble metals. For this purpose, the use of IMCs based on cobalt, iron, and silicon as well as some rare earth elements is proposed.

Methods. IMCs were synthesized using a facility for electric arc melting in a rarefied argon atmosphere. In this work, the following physicochemical methods for the characterization of the IMC samples were used: UV-vis spectroscopy, optical microscopy, SEM, EDX, XPS, and XRD. For electrochemical characterization, impedance spectroscopy and the method for determining the capacitance of the electrical double layer were employed. Linear voltammetry and chronoamperometry were used to determine the optimum conditions for the reactions and ammonia synthesis.

Results and Discussion. The results show the advantages of using electrocatalysts in the form of IMCs, which demonstrate increased values of Faraday efficiency and ammonia yield rates. Schemes of the mechanism of the studied reactions for IMCs and exhaustive clarifications of the actions of electrocatalysts are proposed. The chosen strategy, as well as methods, make it possible to confidently predict the advantages in the NO₃RR reaction.

Acknowledgment. The research was carried out at the expense of the grant of the Russian Science Foundation (RSF) No 25-29-00488, https://rscf.ru/en/project/25-29-00488/.
The authors acknowledge support from Lomonosov Moscow State University Program of Development for providing access to the PS-20 potentiostat–galvanostat with an electrochemical impedance (EIS) measurement module FRA (SmartStat, Russia).

Abstract
The UK government aims to achieve net-zero greenhouse gas emissions by 2050 [1]. Water electrolysers (WEs) represent a promising solution for generating high-purity hydrogen fuel without environmental pollution. Among WE technologies, Anion Exchange Membrane Water Electrolysers (AEMWEs) offer a unique combination of the benefits of alkaline water electrolysers (AWEs) and proton exchange membrane water electrolysers (PEMWEs). However, the performance of AEMWEs heavily depends on precious metal catalysts for the oxygen evolution reaction (OER), making them cost-prohibitive. This study investigates Copper Cobalt Oxide (CCO) spinels as a low-cost, high-performance alternative to precious metal catalysts.

Methods
A hydrothermal synthesis approach, adapted from Abu Talha Aqueel Ahmed et al. [2], was used to synthesise CCO spinels. Reaction parameters, including precursor ratios, temperatures, and synthesis durations, were systematically varied to optimise catalyst composition and morphology. Synthesised materials were characterised using SEM/EDX and XRD to confirm structure and composition.

Results
Physical characterisation revealed the successful synthesis of CCO nanoparticles with distinct morphologies, including flower-like and needle-like structures. Increasing the hydrothermal synthesis temperature to 180°C enhanced purity and homogeneity. Electrochemical testing via cyclic voltammetry (CV) demonstrated that incorporating Cu into the CCO structure improved OER activity, reducing the onset potential and increasing the current density.

Conclusions
This study highlights the potential of CCO spinels as cost-effective, efficient OER catalysts for AEMWEs. The optimised hydrothermal synthesis protocol and resulting nanostructures significantly improved catalytic activity, paving the way for sustainable hydrogen production technologies.

References

[1] UK Hydrogen Strategy, S.o.S.f.B.E.a.I. Strategy, Editor. 2021.

[2] Aqueel Ahmed, Abu Talha, Sambhaji M. Pawar, Akbar I. Inamdar, Hyungsang Kim, and Hyunsik Im. "A morphologically engineered robust bifunctional CuCo2O4 nanosheet catalyst for highly efficient overall water splitting." Advanced Materials Interfaces 7, no. 2 (2020): 1901515

The ongoing and significant growth in global energy demand makes it crucial to develop new, cost-effective, high-quality materials on a large scale to serve as effective electrocatalysts (ECs) in clean energy storage and conversion devices. Among these, fuel cells (FCs) and water splitting devices have emerged as promising candidates. However, their application has been constrained by the reliance on noble metal-based electrocatalysts. In oxygen reactions, specifically O₂ reduction (ORR) and evolution (OER), conventional electrocatalysts are based on noble metals and their oxides, including Pt, Pd, RuO₂, and IrO₂. However, in addition to being scarce and expensive, these materials have poor stability under operating conditions. For this reason, the practical application of these technologies requires the development of efficient electrocatalysis for these processes, which has prompted a recent search for new, cost-effective, and highly active electrocatalysts. Polyoxometalates (POMs) have been proposed as a potential alternative to traditional electrocatalysts, offering a cost-effective solution with high efficiency.

This work involves the preparation of two hybrids based on Dawson Sandwich-type polyoxometalates and multi-walled carbon nanotubes doped with melamine (CoNi3@MWCNT_N8 and NiCo3@MWCNT_N8). The two electrocatalysts exhibited excellent electrocatalytic performance in OER in an alkaline medium (0.1 M KOH), with maximum current densities of 86.70 and 68.32 mA cm 2 and overpotential values of 0.45 and 0.49 V vs. RHE. Furthermore, the two electrocatalysts showed favorable performance in ORR in the same electrolyte, with diffusion limiting current densities of -2.98 and -2.33 mA cm-2 and potential onset values of 0.82 and 0.78 V vs. RHE.

Sodium borohydride is regarded as a potential alternative fuel for direct liquid fuel cells due to its high energy density and ease of handling. However, the efficient electrooxidation of sodium borohydride (BOR) requires the development of advanced electrocatalysts with high activity, low cost, and long-term stability. Transition metal-based catalysts, particularly nickel–iron alloys, have shown considerable promise due to their affordability and favourable catalytic properties. This study explores the synergistic effects of gold and nickel–iron components in achieving high current densities and low overpotentials, which makes these materials promising for applications in direct borohydride fuel cells (DBFCs) and energy storage systems. Herein, we investigate the fabrication, characterization, and electrocatalytic properties of nickel–iron (Ni-Fe) coatings decorated with gold nanoparticles (AuNPs) for BOR. The objective of incorporating AuNPs onto Ni-Fe coatings is to enhance their catalytic activity and stability. Ni-Fe coatings were prepared using two techniques: electroless metal plating and galvanic displacement.

It was determined that AuNPs of a few nanometers in size were deposited on the NiFe coatings through the immersion of a NiFe/Cu electrode in a gold-containing solution for various periods. The BOR was evaluated in 0.05 M and 1 M NaOH solution using cyclic voltammetry and chronoamperometry. The fabricated NiFe catalysts with different AuNP loadings demonstrated significantly higher electrocatalytic activity towards the BOR as compared to bare Au or NiFe/Ti. This indicates the potential of AuNP-decorated NiFe coatings as a promising material for BOR in DBFC applications.

Acknowledgement

This research was funded by a grant (No. P-MIP-23-467) from the Research Council of Lithuania.

Introduction: Environmental pollution, particularly from organic contaminants, poses a growing challenge to public health and the environment. Photocatalysis and electrocatalysis are promising technologies for pollutant degradation, and their integration can enhance the efficiency of this process. Metal–organic frameworks (MOFs) are of increasing interest for such applications due to their high surface area and tunable structure, which can improve both electrocatalytic and photocatalytic performance.

Methods: In this study, a bismuth-based MOF using a 2,6-dicarboxynaphthalene linker was synthesized on an FTO substrate modified with TiO2. The MOF was grown through a reflux reaction in DMF at 110°C for 12 hours. The electrode was characterized using morphological and spectroscopic techniques. Its electrochemical properties were evaluated using chronoamperometry, linear sweep voltammetry, and EIS analysis. Its active surface area and electron transfer coefficient were determined to assess its performance. Its catalytic efficiency was tested in a pH 7 Na2SO4 solution for rhodamine degradation, both in electrocatalytic and photo-electrocatalytic modes.

Results: SEM analysis showed a uniform MOF distribution on the FTO-TiO2 substrate, while FT-IR spectroscopy confirmed carboxylate formation, consistent with the MOF structure. Raman analysis validated the successful formation of MOF and demonstrated its stability post-experiment. Electrochemical tests showed that the Bi-MOF-modified electrodes had a larger electroactive surface area compared to bare TiO2/FTO electrodes. The EIS analysis provided insights into the charge resistance and electrochemical behavior of the system. The Bi-MOF system demonstrated excellent rhodamine degradation, with a photo-electrocatalytic performance surpassing electrocatalysis alone.

Conclusion: The MOF-modified system showed enhanced photo-electrocatalytic properties compared to bare TiO2/FTO electrodes, making it a promising candidate for environmental applications in organic pollutant degradation.

The global economy's sharp growth, extreme fossil fuel consumption and the continuous increase in the population have been forcing the development of more sustainable catalytic processes as well as renewable energy technologies to overcome environmental degradation and the current energy crisis. Unfortunately, renewable energy sources are often unreliable and intermittent, limiting their large-scale applications. Among the most viable electrochemical energy storage and conversion systems are fuel cells, metal–air batteries, and supercapacitors. The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial in electrochemical devices like metal–air batteries and reversible fuel cells [1]. However, these reactions have high activation barriers, limiting the effectiveness of energy conversion devices that use these processes. In addition, both ORR and OER require expensive and scarce precious metal electrocatalysts, making them difficult to use on a large scale. This has stimulated the quest for new, non-expensive, and highly active electrocatalysts during the last few years [2,3].

Therefore, with this in mind, a series of Co/N-doped biochar catalysts were prepared by mechanochemical synthesis using the different parts of Juniperus brevifolia (leaves, bark and wood). Cobalt was chosen taking into consideration the biochar's potential (electro)catalytic performance as ORR and OER electrocatalysts.

Activation under chemical/physical experimental conditions resulted in surface areas of 972 > BET > 145 m2/g. The successful preparation of electrocatalysts was confirmed by XPS, XRD, Raman spectroscopy and SEM/EDS. The best-performing electrocatalyst, Co/N-JBL, showed similar ORR performance to the state-of-the-art Pt/C catalyst. Regarding the OER, Co/N-JBL also showed the most promising results, with an overpotential (η₁₀) of 0.45 V vs. RHE.

[1] C. Freire, D. M. Fernandes, M. Nunes and V. K. Abdelkader, ChemCatChem, 10 (2018) 1703.

[2] R. Ramos, V. K. Abdelkader-Fernández, R. Matos, A. F. Peixoto, D. M. Fernandes, Catalysts, 12 (2022) 207.

[3] I. S. Marques, B. Jarrais, R. Ramos, V. K. Abdelkader-Fernandez, A. Yaremchenko, C. Freire, D. M. Fernandes, A. F. Peixoto, Catalysis Today, 418 (2023) 114080

Reaction Network Analysis and Kinetic Modeling of BHET Depolymerization as (Sub-)Network of PET

Introduction

Polyethylene terephthalate (PET) is widely used in fibers, films, and containers. Due to the low cost of virgin PET and the inferior properties of recycled PET [1-3], recycling remains economically unattractive in many regions [4]. Consequently, large amounts of PET are incinerated or end up in the environment, causing significant ecological damage [5]. Enzymatic depolymerization offers a sustainable alternative with mild conditions, energy efficiency, and environmental benefits [4]. While most studies focus on total depolymerization to terephthalic acid (TPA), this work targets the selective production of intermediates such as MHET and BHET, which are increasingly in demand for PET re-synthesis [6].

Experimental and Modeling

Two enzymes identified from prior screenings [6] were tested in different reaction media to analyze their effects on kinetics, equilibria, and product distribution. Ethylene glycol and DMSO shifted the product spectrum toward MHET. Mechanistic kinetic modeling, considering substrate, enzyme, and product inhibition, was performed to describe the reaction sub-network of BHET depolymerization with high accuracy.

Results and Outlook

A simplified reaction network for enzymatic PET depolymerization was established based on HPLC analysis. Reaction kinetics for BHET depolymerization were successfully modeled, providing a foundation for process design and optimization. Future work will extend the modeling to trimers and dimers and adapt the findings to PEF systems.