Abstract
Earlier research has been primarily focused on WC as one of the most promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER), whereas the other compound in this carbide family—W2C—has received far less attention. Our theoretical calculations suggest that such a focus is misplaced and W2C is potentially more HER-active than WC. Nevertheless, the preparation of phase pure and sintering-free W2C nanostructures represents a formidable challenge. Here we develop an improved carburization method and successfully prepare ultrasmall and phase-pure W2C nanoparticles. When evaluated for HER electrocatalysis, W2C nanoparticles exhibit a small onset overpotential of 50 mV, a Tafel slope of 45 mV dec−1 and outstanding long-term cycling stability, which are dramatically improved over all existing WC-based materials. In addition, the integration of W2C nanoparticles with p-type Si nanowires enables highly active and sustainable solar-driven hydrogen production. Our results highlight the great potential of this traditionally non-popular material in HER electrocatalysis.
Highlights
Earlier research has been primarily focused on WC as one of the most promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER), whereas the other compound in this carbide family—W2C—has received far less attention
We start with the first-principles density functional theory (DFT) calculations to unveil the greater potential of W2C over WC for HER electrocatalysis
The three-state diagram of HER free-energy process in Fig. 1a shows that at the low hydrogen adsorption coverage of 1/4 monolayer (MLH), the DGH on WC is À 0.56 eV, in good agreement with the result reported by Peterson et al and suggesting that hydrogen intermediates adsorb onto WC surfaces more strongly than ideal[25]
Summary
Earlier research has been primarily focused on WC as one of the most promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER), whereas the other compound in this carbide family—W2C—has received far less attention. Tungsten carbide (WC)-based materials have been long advocated and investigated as potential replacements of platinum for HER electrocatalysis ever since the first report by Trasatti more than half a century ago[13] These materials have yet to be capable of replacing precious metal catalysts due to their poor activities: very few have onset overpotentials within 100 mV (refs 7,10,14,15). Due to their chemical inertness, the diffusion rate of carbon atoms from MWNTs to tungsten lattice is slowed down, which leads to suppressed sintering of carbide nanoparticles, and avoids excessive carbon deposition on their surfaces In this way, we are able to achieve the selective synthesis of ultrasmall and phasepure W2C particles with excellent activity and durability for both electrocatalytic and photoelectrochemical hydrogen evolution
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