Boosting the bifunctional electrocatalytic performance of nanowire NiCo2O4@ultrathin porous carbon via modulating the d-band center

Abstract

Developing highly active and stable bifunctional electrocatalysts for the oxidation of alcohols is critical for energy and chemical conversion. Herein, a NiCo₂O₄ nanowire on ultrathin porous carbon (NiCo₂O₄/C) was fabricated and exhibits superior electrocatalytic performance for both hydrogen evolution and benzyl alcohol (BA) oxidation in comparison with pristine NiCo₂O₄ free of carbon. It only needed 1.36 V vs. RHE to afford a current density of 50 mA cm⁻² for BA oxidation. The overpotential for the HER (η₁₀) is −93.0 mV vs. RHE. Furthermore, high yield (96.0%) and faradaic efficiency (98.6%) of benzoic acid were achieved in 10 consecutive stability tests. The outstanding electrocatalytic activity can be attributed to the following aspects: (1) the hierarchical architecture exposed more catalytic active sites and enhanced mass transport; (2) ultrathin porous carbon strengthened the affinity for the reaction medium; (3) strong electronic interactions optimized the energy band structure. DFT simulations proved that the Gibbs free energy of the rate-determining step was reduced when coupling with ultrathin porous carbon, thus lowering the energy barrier and accelerating the reaction process. Theoretical calculations further reveal that the moderate downshift in the E_d energy levels, which balance the adsorption and desorption of the intermediates, is the intrinsic reason for the promoted oxidation activity. This work could provide valuable insights into the design of highly efficient bifunctional electrocatalysts.