Oxygen Evolution Reaction Of Core-shell Nanoparticle Nickel Sodium Phosphate As Electrocatalyst In Alkaline Electrolyte

In the process of electrolyzing water,both the oxygen evolution reaction?OER?and the hydrogen evolution reaction?HER?require a high overpotential when the reaction occurs,which will lead to energy loss.Thus,intensive research is being carried out to develop more cheap electrocatalysts that can shift the potentials of the splitting of water closer to thermodynamic limits.Research on electrocatalysts with high-efficiency catalytic ability for oxygen evolution reaction is the key.Because the oxygen evolution reaction is the bottleneck of the water electrolysis process,it involves four continuous processes at the same time.The existing industrial electrocatalysts for water decomposition are based on compounds or nanoparticles of precious metals?platinum,palladium,iridium,ruthenium?,which leads to their high price.To solve this problem,significant progress has been made over the past few decades and new OER catalysts based on borides,carbides,phosphides,chalcogenides,oxides or hydroxides,complex oxides have been proposed.In recent years,particular attention has been paid to the use of polyvalent metals phosphates and phosphate films for these purposes,which have shown excellent results for both the catalysis of the OER and HER processes.In recent years,for phosphates and their composites,the possibilities of obtaining low overvoltage values for oxygen evolution in an alkaline medium have been demonstrated.At the same time,many questions regarding such electrocatalysts still require further research.Phosphate synthesis was carried out according to two schemes.we were able to obtain this compound in two different forms–the form of nanoparticles and the crystalline form.Here,we investigated hybrid phosphate Na₄Ni₃?PO₄?₂P₂O₇ as a potential candidate for electrocatalysts.We conducted a comprehensive study of Na–Ni–?–O system and obtained single crystals of Na₄Ni₃P₄O₁₅5 without impurities?according to XRD data,PDF card#01-087-0977?.Before further used complex phosphate has been milled in planetary ball mill??btained average size of particles is less than 10 mkm?.With a purpose to estimate stability of this phosphate in the alkaline media,the part of sample was kept in 1 M NaOH solution for 30 days.Analyses performed after treatment indicate that the complex phosphate is partially decomposed.XRD and FTIR spectra data shows that decomposition of phosphate at pH=14occurs with formation of the hybrid Ni?OH?₂-Na₄Ni₃P₄O₁₅5 composite.SEM and TEM observed the formation of nanostructures type shell?Ni?OH?₂?-core(Na₄Ni₃P₄O₁₅).In conclusion,electrocatalysts with excellent activity of hybrid nickel oxyhydroxide phosphates have an overpotential in the range of 280-310 mV at10-20 m?·cm^-2,which is comparable to RuO₂ activity.The result is one of the best for phosphate compounds as catalysts.These results indicate that Na₄Ni₃?PO₄?₂P₂O₇ is one of the best catalysts for electrolysis of water by phosphate compounds.