Study On The Preparation And Performance Of Iron-cobalt-based Catalysts For Oxygen Reduction And Oxygen Evolution Reactions

In the past few decades,environmental pollution and deterioration becomes more and more serious with the rapidly increasing global energy demand,so it becomes more and more important to develop new-generation energy conversion and storage equipment and technologies.For example,fuel cell technology is an important one to convert chemical energy into electrical energy.Meanwhile electrochemical water splitting is a process converting electrical energy into chemical energy which could effectively and environmentally produce hydrogen and oxygen.Therefore electro-chemical water splitting is considered as one of the most promising methods for energy conversion and storage.Among them,oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?are key steps to control the performance of next-generation energy conversion and storage equipment and technologies.It is well known that platinum and its alloys are generally considered to be the best ORR catalysts,while IrO₂ and RuO₂ are considered to be the most effective OER catalysts.However,they all belong to precious metal catalysts and suffer from several problems such as high cost,low abundance and poor stability.Therefore,it is of great significance to explore and develop low-cost,high-efficiency and stable non-precious metal catalysts.Iron and cobalt are earth-abundant transition metal elements with excellent catalytic activity.Based on this,iron-cobalt-based ORR and OER catalysts were designed and synthesized separately by biomass and hydrothermal methods.?1?A facile method for the synthesis of hierarchically nanoporous carbon self-co-doped with Fe and N via the high temperature pyrolysis of pig blood curds?PBCs?promoted by NaCl without any external Fe and N element was reported.Microstructure characterizations illustrated that Fe and N were confirmed to be uniformly dispersed in the as-synthesized hierarchically nanoporous carbon.Electrochemical tests showed that the best forming carbon electrocatalyst exhibited superior ORR catalytic activity with a positive half-wave potential of 0.834 V?vs.RHE?and a high limiting current density of 5.6 mA cm^-2.Furthermore,the as-synthesized carbon electrocatalyst also showed remarkable long-term stability as well as superior methanol tolerance,outperforming Pt/C.The relatively large specific surface area,well graphitization,abundant N active sites and the existence of Fe-N bonds should play key roles in enhancing ORR catalytic activity,indicating that this Fe/N co-doped hierarchically nanoporous carbon is a promising candidate to replace Pt/C.?2?3D porous FeCo oxyhydroxide layer coated on carbon cloth?3D-FeCoOOH/CC?as a highly efficient electrode with a facile and cost-effective electro-oxidation method was successfully synthesized.The Fe doping and in-situ electrooxidation processes successfully introduce the Fe component and produce a unique three-dimensional porous structure,which facilitates the exposure of more active sites and effectively buffers the volume and morphology changes caused by oxygen release.The introduction of Fe greatly enhanced the conductivity and electrochemical active area of the catalyst,which greatly contributed to the enhanced catalytic activity.Electrochemical testing results showed that the as-synthesized 3D-FeCoOOH/CC exhibits a superior OER activity with relatively low overpotential of 259 mV at 10mA cm^-2,small Tafel slope of 34.9 mV dec^-1 and excellent stability in 1.0 M KOH solution,outperforming the commercial IrO₂ catalysts.