Study On Low-Pt And Non-Pt Electrocatalysts Toward Alkaline Hydrogen Oxidation Reaction

Among several types of fuel cells,hydroxide exchange membrane fuel cells(HEMFCs)have attracted attention in recent years.Unfortunately,the HOR kinetics on Pt in basic environment is two orders of magnitude lower than that in acid and a large quantity of Pt is needed to accelerate alkaline HOR,which hinder the development of commercially viable HEMFCs.In this dissertation,four kinds of alkaline HOR electrocatalysts with low or zero Pt content were fabricated.The main conclusions as follows.(1)PtRu nanoparticles with controlled average size of 3.0-3.8 nm uniformly distributed on nitrogen-doped carbon(N-C)were synthesized by a wet-impregnation of nitrogen source chelated-metal cations on carbon support,Ar gas reduction and subsequent NH3 etching method.The variation of activity of PtRu/N-C with Ru molar fractions was investigated,the resultant Pt0.25Ru0.75/N-C exhibits an exceptional alkaline HOR activity(1654 A gptRu-1)and durability.The enhancement in electrocatalytic activity is attributed to the high ECSA(117.3 m2 gPtRu-1),suitable hydrogen binding energy and oxophilic property.The better durability is due to the beneficial effect of nitrogen dopant on stabilizing nanoparticles.A single cell prepared with a low metal loading of Pt0.25Ru0.75/N-C shows a higher peak power density(831 mW cm-2)at a zero back-pressure gas feed,which is 1.8 and 1.1 times that of commercial Pt/C and commercial PtRu/C,respectively.(2)Amorphous NiO decorated Pt NWs with the predominant exposure of Pt(111)facets was synthesized by a one-pot method.Pt/(NiO)NWs with different Pt/Ni molar fractions were prepared by changing the feeding amount of Ni(acac)2.The Pt0.65/(NiO)0.35 NWs/C shows the higher mass specific activity(1340 A gPt-1).In situ electrochemical Raman spectroscopy verifies the existence of OHads intermediates;CO stripping shows Pt0.65/(NiO)0.35 NWs/C has a higher ECSA(89.1 m2 gpt-1),stronger oxophilic property and superb synergistic effect between Pt and NiO active sites in comparison with Pt NWs/C.These collectively account for the remarkable activity of Pt0.65/(NiO)0.35 NWs/C.The fuel cell performance of the Pt0.65/(NiO)0.35 NWs/C shows a peak power density of 830 mW cm-2 superior to that of commercial Pt/C(502 mW cm-2)and comparable to that of commercial PtRu/C(830 mW cm-2)with 0.2 MPa back presssure.(3)A facile synthesis of a series of 2.4-2.9 nm PdIr nanoparticles were evenly distributed on N-C via simple chemical reduction of aqueous metallic complexes in the absence of surfactants.N-C was prepared by heat-treating the mixture of melamine and carbon.The resultant Pdo.33Ir0.67/N-C exhibits an excellent alkaline HOR activity.The mass specific activity(481 A gPdIr-1)and area specific activity(0.45 mA cmPdIr-2)are 1.4 and 1.2 times that of commercial Pt/C,respectively.Electrochemical experiments and density functional theory suggest the high ECSA(106.0 m2 gPdar-1)due to the relatively small average size of the Pd0.33Ir0.67 alloy nanoparticles,appropriate strength of hydrogen binding and oxophilic property originating from an electronic effect among Pd,Ir and N collectively contribute to the high activity of Pd0.33Ir0.67/N-C.When applied as the anode electrocatalyst in a single cell,a peak power density of 514 mW cm-2 is obtained,superior to commercial Pt/C(400 mW cm-2)with 0.1 MPa back presssure.(4)The Ni nanoparticles supported on lanthanum-cerium oxide decorated carbon were synthesized through a two-step approach.Firstly,lanthanum-cerium oxide decorated carbon were synthesized through a coprecipitation process and followed by annealing treatment.Secondly,10.8-12.3 nm Ni nanoparticles were uniformly distributed on the lanthanum-cerium oxide decorated carbon via simple chemical reduction.The as-obtained Ni/La0.5Ce0.5O1.75/C exhibits remarkable HOR performance with the mass specific activity of 8.8 A gmetal-1 and area specific activity of 0.052 mA cmmetai-2,which are 2.9 and 1.8 times that of Ni/C,respectively.The enhanced HOR performance is attributed to the suitable hydrogen binding strength,appropriate oxophilic property and the synergistic effect between oxygen vacancy contained La0.5Ce0.5O1.75 and Ni species.When applied as the anode electrocatalyst in a single cell,a peak power density of 26.8 mW cm-2 is obtained.