The Synthesis Of Fe,Ni-based Electrocatalysts Via Interface Engeering For Alkline Oxygen Evolution Reaction

The global energy crisis and environmental issues make it urgent to develop clean,efficient and sustainable energy conversion and storage technologies.Oxygen evolution reaction(OER)plays a vital role in many renewable energy applications,but limited by the sluggish four electrons transfer process.Thus efficient OER electrocatalysts need to be fabricated to overcome the sluggish kinetic process.Although the most advanced noble metal-based electrocatalysts(e.g.,RuO2,IrO2)have been wildly reported,the high cost and low reserves of noble metals seriously impeded their commercial applications.The cheap and earth-rich tansition metal-based electrocatalysts,especially Fe/Ni-based electrocatalysts,would be good candidates to replace the noble metal-based electrocatalysts.However,most transition metal-based electrocatalysts exhibited poor durability under OER conditions,as well as unsatisfactory catalytic activity.In some cases,the design of OER electrocatalysts must compromises between activity and durability.Thus,there are still some challenges for improving the catalytic activity of tansition metal-based electrocatalysts,while maintaining its durability.Considering about the above problems,we developed a series of strategies based on interface engineering,such as building carbon shell coating on the surface of catalysts,constructing hetero-interfaces in the catalysts and combining the catalysts with carbon supports.The morphology,composition and electronic structure of the catalysts were appropriately adjusted to improve their catalytic activity and durability.It aims to get insight into the relationship between structure and OER peroperty and develop efficient alkline OER electrocatalyts.Several new results in following aspects were obtained:(1)We developed a simple and effective approach to prepare N-doped carbon shell coated Ni2P nanospheres(Ni2P@N-C)with enhanced electrocatalytic durability for OER.Polydopamine-coated Ni nanospheres tranfered into Ni2P nanospheres coated by N-doped carbon shell via one-step annealing treatment,in which NaH2PO2·H2O and polydopamine served as P and carbon source,respectively.The Ni2P nanospheres coated with carbon shell(5 nm)shows much better durability than Ni2P without carbon shell,which can still maitain high electrocatalytic activity after 5000 cycles or 45 hours of long-term testing in the alkaline condition.In addition,the overpotential required for Ni2P@N-C to achieve a current density of 10 mA·cm-2 is only 260 mV,indicating that the appropriate thickness of the carbon shell would not hinder the transfer of active electrons from the internal Ni2P to the surface of the carbon layer.Thus,a suitable carbon shell can provide sufficient physical protection for Ni2P without affecting the electrocatalytic reaction on the surface of Ni2P nanosphere.This method would be a general strategy to develop OER electrocatalysts with enhanced durability.(2)We developed a interface engineering to improve the OER catalytic activity of NiS2 nanospheres by coupling with ferrous phosphites and phosphides(Fe-P).The as prepared NiS2/Fe-P nanospheres possess abundant interfaces which can not only enrich the electroactive sites but also promote the electronic transfer,thus further facilitate the intrinsic activity for OER.Consequently,the optimal NiS2/Fe-P exhibit outstanding OER activity with ultralow overpotential of only 218 mV at the current density of 10 mA·cm-2 and a Tafel slope of 47.5 mV·dec-1.More importantly,it can achieve relatively high current density of 800 mA·cm-2 with overpotential of only 306 mV.(3)We developed a method to prepare hollow FeP/Fe3O4 hybrid nanoparticles supported on carbon nanotubes(CNTs),which could be used as highly active and stable electrocatalysts.The FeP@Fe3O4/CNT hybrids were synthesized by annealing the CNTs adsorbed with Fe(NO3)3,followed by controlled phosphorization treatment.FeP@Fe3O4/CNT catalyst exhibits an outstanding catalytic activity for OER with a low overpotential of only 205 mV at a current density of 10 mA cm-2 and an ultralow Tafel slope of 27.6 mV·dec-1.In addition,FeP@Fe3O4/CNT catalyst also shows good durability,which can still maintain high electrocatalytic activity after 40 hours or 3000 cycles of long-term testing.The excellent OER activity benefits from the electron transfer from Fe3O4 to FeP and good conductivity of CNTs,and the good durability due to the protective effect of the CNTs supports.This work achieved the improvement of catalytic activity while maintaining the durability of the catalyst,indicating that there is no direct inverse relationship between catalytic activity and durability,and it provides a efficient method to design transition metal-based electrocatalysts.