IrNi/C Catalysts For Hydrogen Oxidation Reaction Of Fuel Cells

Proton Exehange Membrane Fuel Cells (PEMFCs) have become increasinglyattractive because of the high energy conversion efficiency, high power density andenvironmental friendly. As one of the key materials for PEMFCs, the research anddevelopment of novel anode catalysts play an important role for the performance andcost of fuel cells. Up to now, platinum-based catalysts are still best commercializedcatalysts and commonly used as anode electrocatalyst in the state-of-the-art PEMFCs.However, high cost, poor performance and comparably complex preparation process ofthose catalysts have hampered their large-scale commercialization. Thus, thedevelopment of high active and cost-efficient non-Pt electrocatalysts in a facil strategyis of great importance in the application and commercialization of PEMFCs.Herein, we report a novel solvent evaporation plus hydrogen reduction (SE-HR)method for the synthesis of high-anode-activty carbon supported IrNi nanoparticles(NPs)(IrNi/C). In this method, deionized water is used as the solvent, and ammonia isused as both a complexing agent and pH regulator. The ammonia was added to thesuspension of metal precursors and leaded Ni to form Ni(NH3)n2+complex cations,while Ir was still in complex anions presented in IrCl62-. Then, the Ir and Ni complexesspontaneously attracted each other by electrostatic attraction to get well distributedNi(NH3)nIrCl6precipitation in the solvent evaporation process. Finnaly, well dispersedcarbon supported IrNi alloy NPs were obtained by in situ reduction and nucleation of Ir,Ni in H2atmosphere.Moreover, we have explored and discussed the optimum technological conditionand mechanism of IrNi/C preparation process. We put primary intesrest in studying onthe influence of pH adjusting reagent, annealing temperature and initial Ir/Nistoichiometric atomic ratio on the morphology and electrocatalytic performances ofIrNi/C. By varying preparation conditions, various IrNi/C samples with the latticeparameter (afcc) of Ir controlled in the range from3.8416to3.6649were prepared.X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectronspectroscopy (XPS), electrode test and single cell test were used to characterize theIrNi/C catalysts. The preliminary results show that:①We have successfully prepared carbon supported IrNi bimetallic alloy by usingthe facile SE-HR method. Uniform sized and spherical shaped sub-3nm IrNi NPs on the carbon support are shown clearly in the TEM image.②The IrNi/C-NH3-500catalyst synthesized by adjusting pH to12with NH3·H2O,and annealing at500C with original Ir/Ni precursors atomic ratio1:1exhibits the besthydrogen oxidation reaction (HOR) catalytic activity among all the IrNi/C samples. Thespecific electrochemical surface area (ECSA) of IrNi/C-NH3-500catalyst is76.7m2g-1Ir, which is larger than that of JM Pt/C (63.6m2g-1Pt). A high limit current density of458A gIrNi-1at0.1V vs RHE is given by IrNi/C-NH3-500, which is even11%higherthan that of JM Pt/C (411A gPt-1). Single cell performance measurements indicate thatthe open-circuit potential of MEA with IrNi/C-NH3-500as anode catalyst is0.97V,almost the same as that of the conventional JM Pt/C MEA. Furthermore, the maximumpower density of the MEA with the non-Pt anode is as high as960mW cm-2, which iscomparable to the commercialized Pt/C catalysts. An average particle size of2.1nm ofthe NPs was identified by TEM. There is no chloride or other residue detected by EDSand XPS, indicating a complete removal of the detrimental species by the facilepreparing and washing procedure.③Interestingly, the mass activity of the IrNi/C for hydrogen oxidation reactionexhibits volcano-shaped dependence on the lattice parameter of Ir with a maximumactivity at approximately3.7325(IrNi/C-NH3-500). We conclude that the optimalIr-Ir bond distance obtained by controlling the synthesis conditions leads to the optimalinteraction between the catalyst surface and the hydrogen intermediates (Ir-Had), andconsequently increases the HOR activity. The high specific ECSA due to the appropriatesize and good dispersion of the as synthesized NPs is also an important reason for theexcellent HOR catalytic activity. This method seems especially efficient for tailoring theproperties of IrNi NPs as one of the promising Pt-alternative catalysts.