Nanoporous RuO2 characterized by RuO(OH)2 surface phase as an efficient bifunctional catalyst for overall water splitting in alkaline solution

Abstract

Abstract With the demand of renewable hydrogen energy, electrocatalytic water splitting is considered as the most promising method for hydrogen production. Herein, a simple synthesis of the nanoporous RuO2 (NP-RuO2) characterized by RuO(OH)2 surface phase was reported. The physical characterization of the materials are achieved by transmission electron microscope (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF) and X-ray photoelectron spectrometer (XPS). For HER activity, the NP-RuO2–450 electrode only needs 87 mV overpotential to obtain a current density of 10 mA cm−2, while RuO2 generates the same current density at a relatively large overpotential (η = 142 mV). Notably, the HER activity of NP-RuO2–450 is also higher than that of Pt (10 mA cm−2, η = 103 mV). The specific activity of NP-RuO2–450 is still 2.4 times higher than that of RuO2 reflecting the enhancement of the intrinsic activity. The OER activity of NP-RuO2–450 electrode has outperformed that of RuO2. The apparent activity of NP-RuO2–450 is 3.5 times that of RuO2 at an overpotential of 270 mV. For the specific activity, NP-RuO2–450 is still 1.9 times higher than that of RuO2. Therefore, NP-RuO2–450 electrode could be used as a bifunctional catalyst for overall water splitting. The excellent HER and OER activities of the NP-RuO2–450 electrode could be attributed to the enhancement of electrochemical surface area of electrode material. However, the more important reason is that the new surface phase creation of hydroxides and the electronic structure modification of Ru.