Rational Regulation of the Defect Density in Platinum Nanocrystals for Highly Efficient Hydrogen Evolution Reaction

Constructing structural defects is a promising way to enhance the catalytic activity toward the hydrogen evolution reaction (HER). However, the relationship between defect density and HER activity has rarely been discussed. In this study, a series of Pt/WO_x nanocrystals are fabricated with controlled morphologies and structural defect densities using a facile one-step wet chemical method. Remarkably, compared with polygonal and star structures, the dendritic Pt/WO_x (d-Pt/WO_x) exhibited a richer structural defect density, including stepped surfaces and atomic defects. Notably, the d-Pt/WO_x catalyst required 4 and 16 mV to reach 10 mA cm^-2, and its turnover frequency (TOF) values are 11.6 and 22.8 times higher than that of Pt/C under acidic and alkaline conditions, respectively. In addition, d-Pt/WO_x//IrO₂ displayed a mass activity of 5158 mA mg_Pt ^-1 at 2.0 V in proton exchange membrane water electrolyzers (PEMWEs), which is significantly higher than that of the commercial Pt/C//IrO₂ system. Further mechanistic studies suggested that the d-Pt/WO_x exhibited reduced number of antibonding bands and the lowest dz²-band center, contributing to hydrogen adsorption and release in acidic solution. The highest dz²-band center of d-Pt/WO_x facilitated the adsorption of hydrogen from water molecules and water dissociation in alkaline medium. This work emphasizes the key role of the defect density in improving the HER activity of electrocatalysts.