Juniperus brevifolia as a potential biomass source for the construction of efficient oxygen (electro)catalysts

Diana Fernandes; Inês Marques; Ana Seca; Andreia Peixoto

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Juniperus brevifolia as a potential biomass source for the construction of efficient oxygen (electro)catalysts

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¹ REQUIMTE/LAQV, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, 4169-007 Porto, Portugal
² LAQV-REQUIMTE, Department of Chemistry, University of Aveiro, Campus de Santiago, Aveiro, 3810-193, Portugal
³ University of the Azores, Faculty of Sciences and Technology, cE3c- Centre for Ecology, Evolution and Environmental Changes, Azorean Biodiversity Group, CHANGE–Global Change and Sustainability Institute, Ponta Delgada, 9500-321, Portugal

Academic Editor: Dominic Alfonso

Published: 21 April 2025 by MDPI in The 3rd International Electronic Conference on Catalysis Sciences session Electrocatalysis

Abstract:

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

Keywords: Biochar; Juniperus brevifolia; oxygen evolution; oxygen reduction;

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