Electrochemical modification and tuning Ni/Ni(OH)2–Ag heterogeneous interface for efficient electrocatalytic hydrogen and oxygen evolution reactions

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A facile and effective method, electrochemical modification and tuning was adopted to prepare the Ni/Ni(OH)2–Ag catalysts with plentiful heterogeneous interfaces. These catalysts performed a synergistic catalytic effect. The catalytic activities towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) were enhanced by appropriate modification of Ni/Ni(OH)2 at Ag electrode surface. Interestingly, the HER activity was further significantly enhanced after electrochemical tuning compared with that of before. Particularly for Ni(10 min)/Ag electrode surface, the overpotential of HER at 10 mA cm−2 (E10mAcm−2) was drastically decreased from −0.372 V to −0.148 V, which is merely 13 mV difference to the value obtained on Pt electrode surface (−0.135 V). Furthermore, the optimized catalyst also exhibited superior catalytic performance towards OER, thus strongly suggesting that it possesses excellent HER and OER bifunctional electrocatalytic activity and stability in alkaline solution. All the results from X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscopy (EDS) mappings and lead-underpotential deposition (Pb-UPD) indicated that more Ag species appeared on the Ni/Ni(OH)2 modified Ag electrode surface and combined with Ni species to form a huge amount of the Ni/Ni(OH)2–Ag heterogeneous interfaces after electrochemical tuning process. It could be the crucial reason for the increase of the number of heterogeneous interfaces.