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

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