Valorization of the inedible pistachio shells into nanoscale transition metal and nitrogen codoped carbon-based electrocatalysts for hydrogen evolution reaction and oxygen reduction reaction

Abstract

Making a consistency with the objectives of circular economy, herein, waste pistachios shells were utilized for the development of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) electrocatalysts which are the key bottleneck in the technological evolution of electrolyzers and fuel cells, respectively. As an alternative to scarce and expensive platinum-group-metal (PGM) electrocatalysts, metal nitrogen carbons (MNCs) are emerging as a promising candidate for both aforementioned electrocatalysis where iron and nickel are the metal of choice for ORR and HER, respectively. Therefore, FeNCs and NiNCs were fabricated utilizing inedible pistachio shells as a low-cost biosource of carbon. The steps involved in the fabrication of electrocatalyst were correlated with electrochemical performance in alkaline media. Encouraging onset potential of ~ 0.88 V vs RHE with a possibility of a 2 + 2 reaction pathway was observed in pyrolyzed and ball-milled FeNC. However, HF etching for template removal slightly affected the kinetics and eventually resulted in a relatively higher yield of peroxide. In parallel, the pyrolyzed NiNC demonstrated a lower HER overpotential of ~ 0.4 V vs RHE at − 10 mA cm⁻². Nevertheless, acid washing adversely affected the HER performance and consequently, very high overpotential was witnessed.