Theoretical and Experimental Investigation of Vanadium Pentoxide-Based Electrocatalyst for Hydrogen Evolution Reaction in Alkaline and Acidic Media

Abstract

One of the key approaches towards better realization of intermittent renewable energy resources, namely solar and wind, is green electrochemical hydrogen production. This occurs through the cathodic hydrogen (HER) and anodic oxygen evolution reaction (OER). In recent years, there has been increasing efforts aimed at developing noble metal-free electrocatalysts that are intrinsically earth-abundant, highly efficient, environmentally sustainable, and inexpensive relative to conventional catalysts. Herein, we investigate V2O5-based electrocatalysts as a candidate for HER. Briefly, the pristine V2O5 is synthesized using a scalable sol-gel method and calcined in air at 450°C for 5 hours. The as-synthesized and postmortem cathodic electrocatalysts were characterized using XRD, SEM/EDS, XPS, particle sizers and electrochemical analyses. The electrochemical analyses entailed standard approaches such as linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), chronoamperometry (CA), and electrochemical surface area (ECSA) to probe relative activities, kinetics, and stabilities under acidic and alkaline environments. Density functional theory (DFT) was used for the quantum mechanical study of bulk and surface electronic and thermodynamic properties, respectively. Surface manipulations through dopant transition metals or anionic oxygen vacancies were also introduced and tested experimentally. The synergy between theoretical and experimental approaches allows for a more fundamental understanding of the different effects in play and complement in explaining the performance trends. DFT analyses revealed that doping the V2O5 and inducing oxygen vacancies can enhance the catalytic HER performance by the creation of new electronic states near the Fermi level and enhancing conductivity. This was showcased through density of states (DOS) and bandgap bulk electronic calculations. Further, based on hydrogen adsorption energy calculations, oxygen deficient or reduced vanadia (R-V2O5) exhibited the lowest adsorption of -0.40 eV. Experimentally, however, R-W0.4V1.6O5 and Zn0.4V1.6O5 were the most active electrocatalyst in acidic and alkaline media, respectively. It was deduced that the presence of certain dopants and/or oxygen deficiencies enhance the electrocatalytic HER performance.