Preparation Of Porous Nickel Electrodes For Electrocatalytic Water Splitting By Phase Inversion Method

Hydrogen is generally considered as a clean and sustainable energy carrier,which is an ideal alternative to fossil fuels for future energy supply.Electrocatalytic water splitting is an environmentally friendly and well-established commercial technology to generate high-purity hydrogen,which involves two half reactions:the hydrogen evolution reaction(HER)and the oxygen evolution reaction(OER).Currently,Pt group metals and the IrO2/RuO2 have the highest activity toward HER and OER respectively with a low overpotential and small Tafel slope.However,they suffer from high cost and low abundance,which limits their large-scale applications in industry.Therefore,effective and economic electrocatalysts made of earth-abundant elements have attracted increasing attention in the field of clean energy.Nickel and nickel-based materials have been proved to be efficient and economical electrodes/electrocatalysts for alkaline water splitting.In addition,commercial Ni foams are often employed as porous substrates for growing nano structured catalysts to achieve an enhanced eletrocatalytic activity.However,research on porous nickel substrates prepared by phase inversion method has not received much attention.Therefore,there is a great potential to develop porous nickel plates prepared by phase inversion and sintering method and further use it for electrocatalytic water splitting.In Chapter one,the research progress of non-noble metal materials(especially for nickel-based materials)for water reduction and water oxidation is discussed.After that,the mechanism and applications of phase inversion method are introduced.In Chapter two,porous nickel electrodes were fabricated by phase inversion and sintering method.The as-prepared nickel electrode contained finger-like straight open pores.The effect of sintering temperature on microstructure and catalytic activity of water reduction were studied.The lower sintering temperature led to a better catalytic activity of water reduction.The porous nickel(900 ?,5h)showed a current density of 10 mA cm-2 and 50 mA cm-2 under an overpotential of 125 mV and 190 mV in 1.0 M KOH with a great catalytic stability and a high Faradaic efficiency-100%.In Chapter three,the catalytic activity of water oxidation of porous nickel(900 ?,5h)was tested 1.0 M KOH.The results showed that the electrode demonstrated excellent performance for OER,with overpotentials of only 300 mV and 362 mV to achieve 10 mA cm-2 and 50 mA cm-2,respectively with a high Faradaic efficiency>92%.Based on the good HER and OER performances,an alkaline electrolyzer using two identical porous nickel electrodes as anode and cathode can be built.The electrolyzer exhibited good electrocatalytic performance and demonstrated a current density of 10 mA cm-2 at a cell voltage of 1.65 V for overall water splitting.In Chapter four,metallic nickel hollow fiber membranes were prepared by phase inversion and sintering method.The microstructure,porosity,bending strength as well as gas flux were characterized.In Chapter five,research presented in this dissertation is summarized,and some suggestions for further research on the preparation of metallic electrodes and modification of porous nickel substrates for water splitting are put forward.