LAUSR

Abstract Transition metal hydroxides for hydrogen evolution reaction (HER) usually have been limited by poor intrinsic activity and weak conductivity. In our work, in situ electro-oxidation as an effective way has been used to modulate the electronic states of active sites for ruthenium hydroxides, which provides obviously enhanced activity for HER in alkaline media. Ag-modified nickel foam (NF) as substrate can provide the excellent conductivity to improve the charge transfer rate of Ru(OH)x/Ag/NF. In situ electro-oxidation process has been conducted for Ru(OH)x/Ag/NF through OER measurements in alkaline media, which results in the formation of more Ru (IV) as higher actives sites for HER. Compared to Ru(OH)x/NF, X-ray photoelectron spectroscopy (XPS) and polarization curves prove that Ag doping in Ru(OH)x/Ag/NF may contribute to the oxidization of ruthenium from Ru (III) to Ru (IV) during in situ electro-oxidation. The obtained Ru(OH)x/Ag/NF exhibits Pt-like HER activity with a very low overpotential of 103.2 mV to drive 100 mA cm−2 in 1.0 M KOH. The excellent stability of Ru(OH)x/Ag/NF has also been demonstrated. Therefore, our work provides a new strategy by modulating valence state of active sites for transition metal hydroxides for efficient HER.