Study On Anode Ni-based Catalysts For Alkaline Polymer Membrane Fuel Cells

The application of precious metal catalysts severely restrict the progress of commercialization for the hydrogen-oxygen proton exchange membrane fuel cells(PEMFCs).Theoretically,alkaline polyelectrolyte fuel cells(APEFCs)can achieve complete non-noble metal electrocatalysis at both anode and cathode,which can reduce the high cost of proton exchange membrane fuel cells fundamentally.There are many significant breakthroughs related to the research on non-noble metal catalysts for the oxygen reduction reaction(ORR)at the cathode of APEFCs,but the research on non-precious metal catalysts for anodic hydrogen oxidation reaction(HOR)has been in stagnation,there are few reports about efficient non-precious metal catalysts for the HOR.Nickle(Ni)as a promising non-precious metal HER/HOR catalyst has limited HER/HOR intrinsic activity under alkaline conditions,what's more,Ni can be easily deactivated by air oxidation.1.By the freeze-drying of the Ni-B/C prepared through the liquid phase reduction method,Ni/C can be synthesized conveniently without the use of surfactant.Ni nanoparticles with ultrafine size(-7nm)are well dispersed on carbon,the loading capacity of Ni is about 50wt%.What's more,Ni/C is resistant to environmental oxidation.This synthesized method could provide a new strategy for the preparation of Ni nano-particles with fine size and strong anti-oxidation ability.2.Ni-Ni(OH)2/C catalysts with different ratio of Ni to Ni(OH)2 can be controllably prepared by a three-step electrochemical treatment.It has been found that Ni(OH)2 modified Ni/C catalysts show obvious HER/HOR enhanced effect,the relationship between the exchange currents of Ni-Ni(OH)2/C and the ratio of Ni to Ni(OH)2 is volcano shaped.At the top of the volcano,the exchange current of Ni-Ni(OH)2/C is 5.8 times higher than that of Ni/C,and the corresponding ratio of Ni to Ni(OH)2 is 0.88(closed to 1).We infer the enhancement is likely to be achieved through a bifunctional mechanism realized by the interface between Ni(OH)2 and Ni.By controlling the partial oxidation of Ni-B/C,it is possible to prepare Ni-Ni(OH)2/C catalyst with high electrocatalytic HER/HOR activity on a large scale.These findings can deepen our understanding of Ni electrocatalytic HER/MOR in base,and provide a new strategy for the preparation of Ni based catalysts with high activity.3.A series of NiMOx/RGO(or XC 72)(M=W,Fe,Mo,Ce,Nb,Zr)composite oxides were synthesized by two universally applicable strategies.It has been found that Ni can be alloyed after the reduction of NiMOx/RGO(M=W,Fe,Mo)at high temperature.The obtained Ni-MoOx/RGO and Ni-WOx/RGO catalysts have better resistance to environmental oxidation,while the introduction of Fe and Nb makes Ni more oxidative;the introduction of ZrO2 can hardly change the antioxidant capacity of Ni in the catalysts.During the process of electrocatalytic HOR,the ability to resist electrochemical oxidation for the Ni-MoOx/RGO decreased with the increase of Mo content.Ni/RGO and Ni-CeO2/RGO could still maintain relatively high HOR current at the potential of 0.3 V(vs.RHE).This study shows the alloying of Ni may improve the ability of Ni to resist environmental oxidation,the ability of Ni to resist electrochemical oxidation can be improved by making use of the interaction between the RGO and Ni.4.The mass exchange current of Ni-MoOx/RGO(1:1)is 8.7mA/mg,which is 1/10 times of that of 5wt%Pt/C,42.5 times improved relative to that of Ni/RGO,and the mass activity is also the highest among all the reported non-noble metal HER/HOR catalysts.Ni-MoOx/RGO(3:1)whose HER/HOR exchange current density is 7.0?A/cm-2 gets the highest HER/HOR intrinsic activity,the intrinsic activity of which is approximately 1/16 times of that of 5wt%Pt/C,and 6-fold increased over that of Ni/RGO.Compared with Ni/C,Ni-CeO2/RGO not only exhibited a strong ability to resist electrochemical oxidation,but also had an obvious increase in the intrinsic activity of electrocatalytic HER/HOR,the enhanced HER/HOR intrinsic activity may be derived from two aspects:the weakening of HBE caused by the interaction between Ni and RGO;the promotion of OH species by CeO2.The introduction of W into Ni/RGO can also significantly improve the electrocatalytic HER/HOR activity of the catalyst,and the enhanced degree of the HER/HOR activity is related to the ratio of Ni to W.The introduction of Fe makes the Ni/RGO lose the electrocatalytic HER/HOR activity.5.Ni/N-RGO and Ni/RGO could be synthesized through the step by step reduction method.It has been found N-doped reduced graphene oxide(RGO)can increase the intrinsic HER/HOR activity of Ni.The exchange current densities of Ni/N-RGO and Ni/RGO are 0.032mA/cm-2 and 0.0167mA/cm-2 respectively.To the best of our knowledge,the intrinsic HER/HOR activity of Ni/N-RGO is the highest among the reported non-noble metal catalysts.The HER/HOR activity of the obtained Ni-P/C was very poor,and the electrocatalytic HER activity of the obtained Ni2P/C was better than that of Ni/C,but it had almost no HOR activity.