Development of hazelnut shell‑derived biochar to support a bifunctional MoCoelectrocatalyst for HER/OER in alkaline medium

Abstract

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), the two concurrent reactions for the electrolytic production of green H2, require low-cost and sustainable electrocatalysts for their scale-up, as for example non-noble metals and carbonaceous structures with high surface area. Our hypothesis is that the activated-doped biochar decorated with Mo and Co provides high porosity and active site dispersion, enhancing HER and OER kinetics with low overpotentials and high stability in an alkaline medium. Here, a bifunctional Mo/Co electrocatalyst supported on N-doped biochar obtained from hazelnut shells has been developed, thus valorizing an agro-industrial residue of major importance in Chile. The activated biochar matrix, with interconnected hierarchical pores, offered a high surface area of 1102 m2 g−1 and ID/IG = 1.08 graphitization, while N-doping was observed by XPS, with the formation of N-pyridinic and N-graphitic functionalities that improved the catalytic performance. The addition of metals to the substrate allowed the formation of bimetallic Mo/Co active sites (Co6Mo6C), increasing the graphitization degree and improved the growth of these bimetallic sites. The electrocatalytic performance in the presence of the metals was good, revealing low overpotentials for HER (0.257 V) and OER (0.370 V) with low Tafel slopes (51 and 59 mV dec−1, respectively) under alkaline conditions, also improving the electron transfer and stability.