WaterSplitting Exceeding 17% Solar-to-Hydrogen ConversionEfficiency Using Solution-Processed Ni-Based Electrocatalysts andPerovskite/Si Tandem Solar Cell

Various noble metal-free electrocatalysts have been explored to enhance the overall water splitting efficiency. Ni-based compounds have attracted substantial attention for achieving efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts. Here, we show superior electrocatalysts based on NiFe alloy electroformed by a roll-to-roll process. NiFe (oxy)hydroxide synthesized by an anodization method for the OER catalyst shows an overpotential of 250 mV at 10 mA cm–2, which is dramatically smaller than that of bare NiFe alloy with an overpotential of 380 mV at 10 mA cm–2. Electrodeposited NiMo films for the HER catalyst also exhibit a small overpotential of 100 mV at 10 mA cm–2 compared with that of bare NiFe alloy (550 mV at 10 mA cm–2). A combined spectroscopic and electrochemical analysis reveals a clear relationship between the surface chemistry of NiFe (oxy)hydroxide and the water splitting properties. These outstanding fully solution-processed catalysts facilitate superb o...