Valence Engineering via Manganese-Doping on Cobalt Nitride Nanoarrays for Efficient Electrochemically Paired Glycerol Valorization and H2 Production

Abstract

Integration of more thermodynamically favorable valorization of biomass (e.g., glycerol), compared to sluggish oxygen evolution, with H2 production is of great significance for energy-saving electrosynthesis of value-added chemicals. However, its widespread deployment has been challenged by costly electrocatalysts and large overpotential reaching an industrial-relevant current density (≥400 mA cm−2). Herein, carbon shell-encapsulated manganese-doped cobalt nitride nanoarrays immobilizing on nickel foam, denoted Mn-CoN@C/NF, are crafted via hydrothermal method and ammoniation. As a bifunctional electrocatalyst, the Mn-CoN@C/NF manifests extraordinary activity for glycerol oxidation reaction (GOR) with an ultralow potential of 1.37 V (versus RHE) at 400 mA cm−2, in conjunction with H2 evolution reaction (HER) with a low overpotential of 31 mV at 10 mA cm−2. A record high Faradaic efficiency (97.7%) for formate production of GOR is delivered at 1.35 V (vs RHE). Impressively, a two-electrode electrolyzer capitalizing on the Mn-CoN@C/NF as catalysts reaches 800 mA cm−2 at 1.83 V, delivering an electricity-saving efficiency of 15.0% compared to pure water splitting. DFT calculations substantiate that Mn species within Mn-CoN not only optimize hydrogen adsorption kinetics for HER, but also elevate Co3+ active sites’ density for GOR. This work offers an energy-saving and efficient electrosynthesis avenue for coproduction of valuable chemicals.