Three-dimensional Porous Micro/Nano Composite Structure NiFeP And Its Electrocatalytic Performance

Hydrogen is regarded as the“ultimate energy”which can replace fossil sources due to its cleanness,high calorific value and renewable energy.The large-scale application of hydrogen depends on whether the preparation method of hydrogen is cost-effective.Compared with other hydrogen energy acquisition methods（fossil fuel reforming,industrial by-product hydrogen,etc.）,water splitting is considered as an effective hydrogen energy acquisition strategy.However,the cheap and efficient catalysts required in water electrolysis are facing challenges.In recent years,transition metal-based compounds have attracted more attention due to their high intrinsic activity and good chemical stability.However,there is still a big gap between the reported catalytic performance of transition metal based compounds and precious metals,which needs further research and development.In this paper,self-assembled Ni Fe O/Nickel Foam（Ni Fe O/NF）nanosheets vertically grow on NF are prepared by a hydrothermal method.The effects of different nickel-iron ratios on the microstructure and electrocatalytic activities of the Ni Fe O/NF are investigated.The results show that the ratio of nickel-iron affects not only the size and state of Ni Fe O/NF nanosheets,but also electrocatalytic activities.With increasing the ratio of nickel-iron,the Ni Fe O/NF exhibits a vertically cross-connected nanosheets structure;this unique structure not only facilitates the transfer of electron/ion,but also increases the catalytic surface area.Moreover,the open space among the nanosheets is conducive to full contact with the electrolyte,and thus the catalytic active sites on the surface and edges of the nanosheets are efficiently used.Also,the open structure is beneficial to the release of hydrogen and oxygen during HER/OER processes.In 1M KOH condition,Ni Fe O/NF exhibits a remarkable OER activity but its HER performance is poor.At 10 m A·cm^-2,the Ni Fe O/NF required OER overpotential of merely is 217 m V,whereas the Ni Fe O/NF required HER overpotential is 210 m V.On this basis,the Ni Fe O/NF with nickel-iron ratios of 3:1 and 4:1 are further phosphatized at low temperature.The results show that at a suitable phosphating temperature,the surface morphology of the Ni Fe O/NF precursor evolved from nanosheets into rod-like structure.The surface consists of Ni Fe P/Ni₂P heterophases.In 1M KOH condition,the Ni Fe P/NF required OER overpotential of 200 m V and HER overpotential of 125 m V at 10 m A·cm^-2respectively.Compared with Ni Fe O/NF,the catalytic activity and stability of the phosphated samples are improved,especially,the HER performance.It is mainly achieved by improving the mechanical strength,increasing the catalytic active sites,and better conductivity and catalytic kinetics after phosphating.Furthermore,the Ni Fe P/NF catalyst also shows efficient overall electrocatalysis with a cell voltage of 1.57 V to drive 10m A·cm^-2.