| Hydrogen energy is regarded as the most potential renewable clean energy,it can replace fossil fuels,alleviate the global energy crisis and increasingly serious environmental pollution problems.Therefore,many researchers have spared no effort to explore a convenient and effective method of hydrogen production.The most prominent strategies are electrocatalysis and photocatalytic water splitting,which are considered as a green and sustainable way to convert water into useful hydrogen(H2)and oxygen(O2).In the electrocatalytic water splitting reaction,compared with hydrogen evolution,oxygen evolution reaction(OER)needs a larger overpotential to drive.Therefore,the OER is a rate-limiting step for the whole electrolytic water splitting reaction.At present,noble metal RuO2 and IrO2 are highly active for OER,but the high costs restrict their applications.Therefore,people have been devoted to the exploration of electrocatalysts with low overpotential and high current density.In photocatalytic water splitting,due to the low separation efficiency of photogenerated cariers,and the small absorption range of light,the practical application of semiconductor is seriously hindered by the problems.Therefore,people are making efforts to improve the performance of the photocatalyst by using ion doping,semiconductor recombination,dye sensitization and co-catalyst modification.In recent years,transition metal nitrides have been widely studied due to their metal-interstitial electronic structure and they have good metal conductivity.Among the nickel nitride,have unique advantages such as non-toxicity,low cost,high chemical stability and platinum-like properties,and are a promising catalyst material.In this paper,the development of nickel nitride-basad composite photo-and electro-catalyst is studied.The main research contents are as follows:(1)Holey sheets of ultrathin carbon-coated nickel nitride(Ni3N@NC)were successfully prepared via a facile polymerization and in situ nitridation strategy.Ni3N@NC exhibit outstanding oxygen evolution reaction(OER)performance as well as high long-term durability in alkaline electrolyte.The significant OER activity and stability are mainly ascribed to(Ⅰ)ultrathin oxide layers as active sites confined between the Ni3N core and outside carbon coating,(Ⅱ)overoxidation of Ni3N suppressed by carbon coating synthesized in situ to improve the stability for OER,and(Ⅲ)strong coupling of Ni3N particles with an ultrathin carbon coating derived from in situ nitridation to efficiently promote fast electron transfer.This catalyst design strategy will greatly aid in the development of highly active OER electrocatalysts in the near future.(ii)Co-precipitation method followed by nitridation is used for fabricating highly efficient and stable Au decorated-Ni3N(Au/Ni3N)electrocatalyst for OER activity in alkaline solution.The Au/Ni3N-10 with best catalytic performances observed when the loading content is about 2 wt%.From experimental and theoretical calculations,it is found that Au nanocluster doping onto Ni3N can effectively regulate Ni3N electronic structure,and reduce the energy barrier associated with OER activity,and exhibits the higher OER activity.(iii)NiO-Ni3N/g-C3N4 heterostructures have been in-situ fabricated by a hydrothermal method followed by calcinations process for photocatalytic hydrogen production.The results showed that the optimized NiO-Ni3N-1.5/g-C3N4 exhibited the best photocatalytic activity for hydrogen evolution,at the same time,the hydrogen evolution rate of this photocatalyst is very close to that of the best noble metal based photocatalyst(1 wt%Pt/g-C3N4).Under the light of illumination,the photo-generated electron-hole pairs excited by the NiO-Ni3N/g-C3N4 present a Z scheme reaction path,so that the whole reaction system exhibits a stronger oxidation-reduction capability and exhibits the highest photocatalytic hydrogen evolution activity. |
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