Nb doping strategy for active site modification in Co3O4 to enable concurrent hydrogen production and glycerol valorization for efficient formate production

Abstract

The electrocatalytic glycerol oxidation reaction (GOR) has emerged as a sustainable and energy-efficient alternative to the oxygen evolution reaction (OER), offering the dual advantage of hydrogen (H₂) generation through the hydrogen evolution reaction (HER) and selective upgrading of biomass-derived glycerol into value-added chemicals like formate. However, to address the contemporary challenge of developing low-cost and stable electrocatalysts for the GOR we have synthesized a niobium-doped cobalt oxide (Nb-Co₃O₄) based electrode with a binder-free approach. Herein, we report Nb–Co₃O architecture (designated as 3NCO for 3% doping of Nb) on nickel foam (NF) via a hydrothermal strategy, serving as a high-performance, bifunctional electrocatalyst for the HER, OER, and GOR. Nb incorporation into the Co₃O₄ lattice, evidenced by XRD peak shifts, Raman mode alterations, and XPS valence changes, introduces lattice distortion and electronic modulation, and FESEM morphological advancements, which collectively enhance active site density and charge transfer kinetics under alkaline conditions. As a result, the 3NCO/NF electrode exhibits excellent activity, requiring only 196 mV overpotential to achieve 10 mA cm⁻² for the HER, and 1.50 V vs. RHE for the OER in 1 M KOH. Notably, in 0.1 M glycerol + 1 M KOH, the GOR proceeds at just 1.19 V vs. RHE, achieving a remarkable potential drop of 330 mV compared to the OER, and enabling overall electrolysis at 1.46 V in a two-electrode system. This work highlights the role of lattice Nb doping in boosting active site availability and electron transfer, positioning 3NCO/NF as a robust platform, by sustaining more than 90% of faradaic efficiency, for energy-saving H₂ production and electrochemical glycerol valorization.