Surface Engineering Of Nickel-based Foam Electrodes And Their Performance Of Electrolysis Of Water

Hydrogen production from electrolysis of water has attracted much attention because of its green and pollution-free production.Alkaline water electrolyzer is currently the mainstream of commercial equipment for hydrogen production by electrolysis of water,which has the advantages of low equipment cost and high product purity.However,the disadvantage of low energy efficiency of alkaline water electrolyzers limits their large-scale application.The main factor limiting its energy efficiency is the slow electrode reaction,especially the anodic oxygen evolution reaction.Finding catalysts with excellent performance is key to solving this problem.The existing commercial alkaline water electrolyzer mainly consists of nickel-based catalyst,which has the advantages of low price,high reliability and long life.However,its catalytic activity still needs further improving so that it can reach,or even exceed the performance of commercial noble metal based catalysts.Nickel-based materials are flexible and easy to process,with large specific surface area and rich pores conducive to mass transfer,which is a good choice of material for catalytic electrodes.Meanwhile,the industrial application of catalytic electrodes demand the electrodes’properties of stability,economy,high performance and simple preparation process.Based on the review of previous research,this dissertation seeks a simple,environmentally friendly and low-cost surface modification process for the purpose of realizing industrial application,modifies nickel foam,and improves the catalytic activity of nickel foam,thereby reducing the energy consumption of alkaline water electrolyzer and promoting the large-scale application of alkaline water electrolyzer.The specific research content is as follows:（1）A layer of Fe OOH was modified on the surface of nickel foam by quenching in iron nitrate solution,and the catalyst obtained was named Ni-Fe.In the oxygen evolution reaction（OER）test,Ni-Fe reached a current density of 100m A cm^-2 at an overpotential of 284 m V,which improved the oxygen evolution performance of nickel foam,and could stably serve for more than10 h at a current density of 20 m A cm^-2 without significant degradation.Its good oxygen evolution performance is attributed to the following factors:（I）the surface of nickel foam modifies a layer of Fe OOH,which increases the specific surface area and active sites of nickel foam,and creates a heterogeneous interface between Fe OOH and Ni.（II）The prepared Ni-Fe electrode has better hydrophilicity than nickel foam,which makes the bubbles on it escape from the active site faster,prevents the bubble retention and aggregation from hindering the contact between the active sites and the reactants,and reduces the catalytic active material shedding caused by the impact of large bubbles,thereby increasing the efficiency and service life of the active sites.（2）In order to reduce the huge energy consumption caused by the high-temperature process and further improve the performance and stability of the catalytic electrode,we developed a simpler salt baking method for surface modification of NiMo alloy foam（NiMo）.In this method,Fe OOH is assembled on the surface of NiMo by the solid phase reaction of iron nitrate nonahydrate solid with NiMo to improve the overall water decomposition performance of NiMo foam.Compared with the traditional electrocatalyst synthesis method,the salt baking method proposed by us can be carried out at room temperature and pressure,without the use of reaction solvents,thereby avoiding the adverse effects of high temperature and high pressure,complex processes and environmental pollution.When used as an OER electrocatalyst,NiMo-Fe has an overpotential of 280 m V at a current density of 100 m A cm^-2.In addition,the current density generated by a water electrolyzer made of NiMo-Fe is approximately 2.5 times that of a water electrolyzer made of NiMo,providing performance close to the level of Pt/C||Ru O₂.In addition,the NiMo-Fe electrode can maintain the oxygen evolution current density of 25 m A cm^-2 for more than 50 h,showing good stability.The excellent water electrolysis performance of NiMo-Fe may be caused by the following factors:（I）During the salt baking process,corrosive Fe（NO₃）₃·9H₂O accumulates on the surface of NiMo foam,which increases its surface roughness.At the same time,a thin layer of flower-like Fe OOH was formed on the surface of NiMo foam,which increased the specific surface area of the electrode,constructed a Fe OOH/NiMo heterogeneous interface,and generated a new active site.（II） Salt baking treatment enhances the hydrophilicity of NiMo foam,so that the bubbles adhered to the electrode can quickly detach from the electrode.（3）The second work of the salt baking method avoids the energy consumption caused by the high-temperature process,but its still requires a preparation time more than 24 h.In order to further simplify the preparation process,Feand Ni co-deposition on nickel foam by electrodeposition method was used to make Ni-FeNi catalytic electrode,and the process of Fe and Ni co-deposition was optimized through exploration experiments,and the three-dimensional "jungle"composed of rough rod-like FeNi-LDH（FeNi-layered double hydroxide）was modified on the surface of the electrode to construct rich oxygen evolution active sites,which were conducive to the diffusion of gas products.Compared with the quenching process and salt baking process mentioned above,the electrodeposition method can avoid the energy consumption caused by high temperature,and can quickly and conveniently adjust the composition of the active sites.At the same time,the appropriate doping of Fe can significantly increase the oxygen evolution activity of Ni（OH）₂.As an OER catalyst,Ni-FeNi only requires an overpotential of 268m V to achieve a current density of 100 m A cm^-2,a Tafel slope of 61 m V dec^-1,and stability of more than 60 h at a current density of 630 m A cm^-2.