With the rapid consumption of fossil fuels and environmental pollution, it is imperative to develop renewable energy. Hydrogen is expected to replace traditional fossil fuels because of its clean and renewable characteristics. The key to the deep utilization of hydrogen energy lies in the low-cost and large-scale preparation of hydrogen. Hydrogen production by electrolysis of water is one of the effective ways, but its anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) still show high overpotential, which greatly limits the efficiency of hydrogen production by electrolysis of water. So far, precious metal materials Pt/C and IrO2 are efficient catalysts for HER and OER respectively, but their high price and limited storage limit their large-scale application. Although the research of non noble metal HER and OER catalysts has made a series of progress, there are still some challenges. For example, how to prepare highly active multi-stage nanostructured electrodes in a simple and large-scale way to achieve full water electrolysis under high current density is still one of the problems and challenges to be solved.
Recently, the research team of Hu Jinsong, a researcher of the Institute of Chemistry of the Chinese Academy of Sciences, cooperated with Professor Li Jihui of Hebei Normal University, and reported a simple chemical etching method, in which industrial NiAl alloys are immersed in strong alkaline solutions. Because metal Al is easy to be etched by strong alkaline solutions, and metal Ni is easy to react with strong alkaline, Ni (OH) 2 nano sheet arrays are directly generated on the NiAl alloy substrate, A multi-stage framework Ni (OH) 2/NiAl with high porosity is formed. Electrochemical studies showed that the framework exhibited good OER catalyst performance, and the overpotentials at current densities of 10 and 100 mA cm-2 were 289 and 425 mV, respectively. On this basis, the researchers deposited NiMo alloy with higher activity for hydrogen evolution reaction and NiFe alloy with higher activity for oxygen evolution reaction on the Ni (OH) 2/NiAl active skeleton respectively by a simple electrodeposition method, and obtained more efficient hydrogen evolution electrode NiMo/Ni (OH) 2/NiAl and oxygen evolution electrode NiFe/Ni (OH) 2/NiAl through the composite of active material and three-dimensional multi-stage active bone frame structure. The overpotential of the obtained composite hydrogen evolution electrode at 10 mA cm-2 is only 78 mV; And the overpotential of the composite oxygen evolution electrode at the current density of 10, 100 and 500 mA cm-2 is only 246, 315 and 374 mV respectively. The cell voltage of the electrolyzed water device composed of these two electrodes under alkaline conditions is only 1.59 V at a current density of 10 mA cm-2.
Because the preparation method of the electrolytic water electrode in this research work is extremely simple, and the raw materials are easy to obtain, the high efficiency water electrolysis can be achieved by directly immersing industrial NiAl alloy in alkaline electrolyte. At the same time, the design of multi-stage electrode structure is conducive to the realization of electrolytic water under current density, so it is very convenient for large-scale preparation and practical industrial application, and is expected to achieve large-scale production and application. This method of etching industrial alloys to prepare electrodes of electrochemical devices with multi-level nanostructures also provides a new idea for designing other highly active electrodes.