Nanocolumn Supported By NiMoO₄ On Nickel Foam For High Stability And Low Overpotential Hydrogen Production

The energy crisis and the seriousness of environmental pollution urgently urge us to develop renewable and clean energy sources.Unfortunately,the current production of hydrogen is mainly dependent on steam methane reforming and coal gasification.There can be no doubt that we are using up non-renewable fossil fuels and it may cause carbon emission.Furthermore,this reaction cost a lot of energy consumption and the production is not purity.Among various new renewable energy sources,hydrogen is expected to play a key role in future due to its high gravimetric energy density,environmental friendliness,and earth-abundance.Water electrolysis is considered as one of the most environmentally friendly and efficient strategies to produce high purity hydrogen,especially when electricity is from renewable energy sources.Pt-based materials,as the most active electrocatalysts toward the Hydrogen evolution reaction(HER),exhibit the advantages of low overpotential and low Tafel value.However,the scarcity and high cost of Pt are still the hurdle for its widely industrial applications.Therefore,it's high desirable to develop earth-abundant and high activity alternatives to Pt-based as HER electrocatalysts.In recent years,huge effort has been put into developing nonprecious metal electrocatalysts with low cost and high efficiency.The metal alloys,oxides,chalcogenides,nitrides,phosphides carbides,borides have been intensively researched.Some of electrocatalysts have exhibit extremely high activity in HER reaction even comparable to that of Pt-based electrocatalysts.It should be mentioned that nanomaterials usually have Dual characteristics(poor stability and high reactivity).Nowadays,most of researches mainly pay close attention to the high activity of electrocatalysts,whereas the poor stability of nanomaterials have not been concerned.The stability and long-term durability are extremely significant index with respect to the industrial production.Therefore,at the moment most electrocatalysts don't have enough stability to deal with industrial production.Thus,it's suggested that a competent HER electro-catalyst should possess four characters as follows(1)Cheap and easy to get,using earth-abundant elements to reduce its cost.(2)Excellent electrochemical performance as well as Pt-based electrocatalysts.(3)Long time stability,full water electrolysis experiments not less than 1000 h and anti-oxidative intermittent test.(4)Wide range of pH,very stable and in both acid and alkali.Which is indispensable in real industrial production.1.Preparation of NiMoS/NF materials:Firstly,a simple one-step hydrothermal method using ammonium molybdate and nickel nitrate as the precursor solution to synthesize the nano-column precursor NiMoO4 on the nickel.Secondly,sulphur was placed on the upstream side of the furnace as the source of S,followed by placing the as-prepared NiMoO4/NF in a separate porcelain boat on the downstream side.The optimal reaction conditions were determined by optimizing conditions such as temperature,constant time,and quality of sublimed sulfur.NiMoS/NF was synthesized at 300? and a mass ratio of precursor to sublimation sulfur of 1:2 at a constant temperature of 120 min.Only in this way NiMoS/NF can have excellent catalytic activity and excellent physical and chemical stability.Its overpotential at a current density of 10 mA/cm2 is 89.4 mV,which is comparable to other research results during the same period.2.Preparation of NiMoN/NF materials:The preparation steps of NiMoO4/NF are the same as the above,this chapter is mainly for the study of N doped NiMoO4/NF.The nitrogen source I selected dicyandiamide,urea,ammonia,melamine and other organic nitrogen-containing compounds.Detailed plans were made to find the best reaction condition on the reaction temperature of pyrolysis and nitrogen,constant temperature time,nitrogen source quality and other aspects.NiMoN/NF synthesized at 600? with a mass ratio of precursor to dicyandiamide of 1:3 at a constant temperature of 120 min exhibited excellent hydrogen evolution reaction performance and remained stable in strong acid and strong alkaline electrolytes.Its hydrogen evolution overpotential at current densities of-10 mA cm-2 and-100 mA cm-2 is only about 5.0 mV and 60.0 mV,and its Tafel slope is only 45.4 mV dec-1.Demonstrated electrocatalytic activity and stability superior to precious metal Pt/C.3.Industrial amplification experiment:The NiMoN/NF catalyst optimized by the above work was used for small-scale scale-up experiments in the laboratory,and the NiFe/NF prepared by electrodeposition method was used as the anode to form full-water electrolysis.In this section,the 1 cm*1 cm electrocatalyst in the laboratory was successfully enlarged by 100 times using the above method.The electrolysis was tested at 85? high temperature and 30%KOH strong base.Different substrate materials and diaphragm materials were investigated.And an aging experiment up to 1600 h was tested at room temperature to verify the excellent electrocatalytic activity and stability of the material.The Combination of producing has laid a laboratory foundation for the future industrialization of electrolyzed hydrogen production.