Preparation And Performance Of Transition Metal Iron-based Electrocatalysts For Oxygen Evolution Reaction

As carbon-neutral policies push forward,people are urgently looking for renewable energy sources.Hydrogen energy has intrinsic high energy density and H₂ combustion can achieve zero CO₂ emission.These properties make H₂ becoming an ideal alternative to fossil fuels.By comparsion with biological hydrogen production,industrial by-product hydrogen production,photocatalytic hydrogen production and other hydrogen production means,electrocatalytic water cracking hydrogen production based on environmentally friendly,products with high purity and other characteristics stands out.The development of water electrolysis technology has been hampered by slow kinetics of oxygen evolution.Developing non-noble metal oxygen evolution catalysts with low price,high activity and excellent stability is the key to promote development of water electrolysis technology.Four kinds of transition metal Fe-based electrocatalysts are prepared by electrodeposition,electrodeposition and high temperature pyrolysis.Their physical characteristics and electrocatalytic oxygen evolution performance are studied under alkaline conditions.The main contents are as follows.（1）Bacterial cellulose based carbon nanofibers（BCCNF）with 3D network structure are prepared by high temperature pyrolysis of freeze-dried bacterial cellulose.On this basis,Fe-Co-B nanosheet is successfully anchored to BCCNF（Fe-Co-B/BCCNF）by electroless deposition.The effects of different molar ratios of Fe Cl₃ 6H₂O and Co Cl₂ 6H₂O on catalytic performance of the prepared catalysts are studied in 1.0 mol L^-1 KOH solution.When Fe/Co molar ratio is 1:3,electrocatalytic oxygen evolution performance of the prepared ternary Fe-Co-B is significantly enhanced compared with that of the binary Fe-B and Co-B.Fe-Co-B/BCCNF requires an overpotential of only 160 m V（η）to achieve a current density of 10 m A cm^-2（j）.In addition,current density attenuation of prepared ternary Fe-Co-B can be almost negligible during the 36 h chronoamperometry test,showing good stability.（2）The nickel foam grafted with graphene aerogel（GA@NF）is prepared by freeze-drying.Then,Fe-Ni-P/GA@NF electrocatalyst is obtained by in-situ growth of tremella-like Fe-Ni-P nanosphere on GA@NF by electroless deposition.With increasing Fe Cl₃ 6H₂O content in raw material,oxygen evolution activity of Fe-Ni-P/GA@NF initially increases and then decreases.When molar ratio of Fe Cl₃ 6H₂O to Ni Cl₂ 6H₂O in raw materials is 3:2,the prepared Fe-Ni-P/GA@NF exhibits low overpotential(j=50 m A cm^-2,η=320 m V).In addition,Fe-Ni-P/GA@NF exhibits excellent stability in 24 h chronoamperometry test.（3）A series of vanadium ferrocyanide（VHCF/GA）supported by graphene aerogel are prepared by freeze-drying.Prussian blue analogues-based Fe-V-P/GA is further prepared by high temperature pyrolysis.The effect of molar percentage of VCl₃ and K₃[Fe（CN）₆]on electroactivity of oxygen evolution reaction is studied.When the molar percentage of Fe/V in raw material is 1:1,the prepared Fe-V-P/GA exhibits lower overpotential(j=10 m A cm^-2,η=234 m V)than other prepared catalysts.Additionally,current density of Fe-V-P/GA remains at 93.45%during chronoamperometry test for 70 h,indicating that it has excellent stability.（4）Fe-B-P/NF is prepared by electrodeposition using NF as substrate and Fe Cl₃ as iron source.The results show that catalytic activity of Fe-B-P/NF increases first and then decreases with increasing Na BH₄ content in raw materials.When molar ratio of Na BH₄ to Na H₂PO₂ H₂O is 7:3,Fe-B-P/NF materials exhibit excellent OER catalytic performance(j=10 m A cm^-2,η=253 m V).Furthermore,Fe-B-P/NF catalyst showes excellent stability in 24 h chronoamperometry test.The results above indicate that four transition metal Fe-based electrocatalysts exhibit excellent electrocatalytic oxygen evolution performance in alkaline environment and they are valuable catalysts for oxygen evolution reaction.