Optimizing the Atom Substitution of Er in WS₂ Nanosheets for High-Performance Photoelectrochemical Applications

Abstract

Introducing the density of states or defects within the band gap in two-dimensional nanomaterials by rare-earth (RE) element substitution would make them potential candidates for application in next-generation optoelectronic devices. Furthermore, doping with RE elements possessing fine-structured spectral emission and absorption can improve the fundamental research and technological applications of two-dimensional nanomaterial-based photoelectrochemical (PEC) activity due to abundant active sites and low interfacial contact resistance with the electrolyte. Herein, an Er-doping strategy is utilized for the synthesis of Er-doped WS2 nanosheets to simultaneously achieve both upconversion and downconversion emissions, which can efficiently absorb more solar light for PEC activity. We first report a two-step method combining magnetic sputtering and sulfurization to synthesize Er-doped WS2 nanosheet-based electrodes. The effect of Er doping into a single-phase hexagonal-structured WS2 (p-type semiconductor)-based electrode on PEC activity is investigated and compared with pristine WS2 counterparts under one standard sun condition. Results indicate that a photocurrent density of −20 μA·cm–2 at −0.21 V versus RHE (reversible hydrogen electrode) with an enhancement factor of ∼200-fold due to a wider absorbance range (400–808 nm) and a decreased overpotential for hydrogen reduction are achieved. Moreover, the resistance of the Er-doped WS2 electrode is found to be decreased from 500 to 28 kΩ, with nearly a 20-fold decrease compared with that of the pristine WS2 counterparts, contributing to the higher efficiency in electron transfer into the electrolyte. The mechanism is confirmed by Monte Carlo simulations and first-principles calculations. The Er-doped WS2 nanosheets are therefore a promising substitute for noble metals in PEC applications.