Novel Selenide Composite as an Effective Bifunctional Electrocatalyst for Energy-Saving Hydrogen Production through Methanol-Assisted Water Electrolysis

Hydrogen, as the cleanest fuel, is the cathodic product of water electrolysis. The hydrogen evolution reaction (HER) in the cathode is coupled with the oxygen evolution reaction (OER) in the anode of the electrolysis cell. However, highly efficient and economic catalysts are required for the HER and especially for the OER to proceed at reduced voltages. Recently, in a new effective strategy, the OER has been replaced by methanol oxidation reaction (MOR) which is more favorable, thermodynamically, but still needs efficient catalysts. Herein, a new composite is proposed as a bifunctional electrocatalyst for both HER and MOR which is a multimetal selenide formed on nickel foam (NF). A metal-organic framework (Ce-MOF) was used as the cerium ion source and as a self-sacrificing template for the preparation of Ce/Co/Ni selenides in a flower-like porous structure. Characterization of the composite was carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and electrochemical methods. The prepared CeSe/Co3Se4@NiSe-NF showed excellent catalytic activity toward both MOR and HER. When CeSe/Co3Se4@NiSe-NF was used as the anode in an alkaline methanolic solution in a 3-electrode cell, an ultrahigh current density (135.6 mA cm-2) was obtained at a low working potential of 1.45 V (vs RHE) and a small Tafel slope (73.3 mV dec-1). When the catalyst was used as the cathode, a small overpotential (121 mV to pass 10 mA cm- 2) and Tafel slope (65.5 mV dec-1) were obtained during HER. Finally, a hybrid water-electrolysis cell (two-electrode system) was designed using CeSe/Co3Se4@NiSe-NF both as cathode and anode electrodes (in 1.0 M NaOH + 0.5 M methanol) which delivered a current density of 10 mA cm- 2 at a low cell voltage of 1.45 V (vs RHE). The coelectrolytic cell exhibited excellent stability for at least 20 h. Density functional theory (DFT) calculations illustrated the effectiveness of using CeSe, as the most accessible layer for HER and MOR, and confirmed the more facile electron transfer of the composite compared with each of the layers. This study offers a new strategy to design Ce-based selenides as bifunctional electrocatalysts with superior electrocatalytic performance in methanol-assisted hydrogen production cells.