The shortage of fossil energy reserves and the problems caused by environmental pollution prompt us to accelerate the pace of green energy research. Hydrogen has been regarded as an ideal green energy due to its high mass energy density and non-polluting combustion product. As a source of green hydrogen, water electrolysis has been widely concerned and its bottleneck mainly lies in how to develop efficient catalysts. Tungsten phosphide (WP) is believed to be a promising electrocatalyst in the electrochemical hydrogen evolution reaction (HER). Metal doping is one of the common methods for its modification, but the dopants often appear in the form of atoms and have weak interaction with the active phases. In this study, Co-doped carbon-supported WP was modified by a citric acid-assisted two-step aging method and compared with the traditional one-step aging method and the non-aging method for HER. The delicate temperatures (50 °C favors complexation of Co, while 90 °C is conductive to W) of the two-step aging enable the dopant Co to intrude the lattice of WP without causing agglomeration of WP particles and carbon support. Meanwhile, strong electronic metal-supported interaction (EMSI) also exhibited between the catalyst and the support. Under acidic condition, CoWP-CA/KB (two-step aging) only required an overpotential of 111 mV to reach a current density of 10 mA cm<sup>-2</sup> and showed neglectable current decay for more than 50 hours. Its remarkable performance results from the delicate particle size, uniform dispersion, lattice distortion, and abundant defect sites. Moreover, seven industrially used carbon supports are adopted to verify the universality and industrial application prospect of this method. This novel synthesis strategy will be pivotal for designing robust metal doped supported electrocatalysts with high HER activity and durability to meet the future keen demand for hydrogen.

Two-step aging method: An efficient strategy for metal doping

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