Grain-Boundary-Rich RuO 2 Porous Nanosheet for Efficient and Stable Acidic Water Oxidation.

RuO 2 has been considered as the most likely acidic oxygen evolution reaction (OER) catalyst to replace IrO 2 , but its performance, especially long-term stability under harsh acidic conditions, is still unacceptable. Here, we propose a grain boundary (GB) engineering strategy by fabricating the ultrathin porous RuO 2 nanosheet with abundant of grain boundaries (GB-RuO 2 ) as an efficient acid OER catalyst. The involvement of GB induces significant tensile stress and creates an unsaturated coordination environment, effectively optimizing the adsorption of intermediates and stabilizing active site structure during OER process. Notably, the GB-RuO 2 not only exhibits a low overpotential (η 10 =187 mV) with an ultra-low Tafel slope (34.5 mV dec -1 ), but also steadily operates for over 550 h in 0.1 M HClO 4 . Quasi in situ/operando methods confirm that the improved stability is attributed to GB preventing Ru dissolution and greatly inhibiting the lattice oxygen oxidation mechanism (LOM). A proton exchange membrane water electrolysis (PEMWE) using the GB-RuO 2 catalyst operates a low voltage of 1.669 V at 2 A cm -2 and operates stably for 100 h at 100 mA cm -2 .