【摘要】 采用循环伏安扫描测试对不同浓度的甲酸在纳米Au颗粒((10.0±1.2)nm)承载Pt电催化剂(记为Ptm^Au,其中m为Pt/Au原子比)上的电化学氧化过程进行了研究.结果表明,Pt在纳米Au颗粒表面的形态对甲酸的电化学氧化行为影响显著.当Pt对Au颗粒形成壳层覆盖(m>0.2)时,甲酸电氧化反应主要发生在高电势(相对SCE电极为0.6~1.0 V)范围,与常规Pt/C电催化剂上甲酸的电氧化行为类似;当Au表面Pt的形态由单原子壳层(m=0.2)递变为不大于1.0 nm的Pt原子簇或原子筏(m<0.2)时,在低电势(-0.2~0.6 V)范围也能明显检测到甲酸的电氧化反应,而且随着m的减小,Pt的质量比活性显著提高.Pt呈现100%暴露(电化学活性面积EAS=236 m2/g-Pt)的Pt0.05^Au/C电催化剂在甲酸电氧化峰(0.38 V)处的质量比活性是通常Pt/C电催化剂(Pt分散度为30%或EAS为74 m2/g-Pt)的40倍,表明随着Au颗粒上Pt尺寸的减小或分散度的提高,Ptm^Au/C电催化剂对甲酸电氧化反应的催化活性也显著提高.在甲酸浓度由0.2 mol/L渐提高至3.2 mol/L时,Ptm^Au/C和Pt/C催化剂上甲酸电氧化反应的比电流均呈先增大后减小的火山形变化,表明适宜的甲酸工作浓度也是在Pt基催化剂上实现高功率直接甲酸燃料电池的关键因素之一.更多还原

【Abstract】 Nanostructured Pt-on-Au electrocatalysts(coded as Ptm^Au,m shows the atomic Pt/Au ratio) were prepared by deposition of Pt on colloidal Au particles((10.0±1.2) nm) and then employed for electro-oxidation of formic acid at concentrations of 0.2-3.2 mol/L by cyclic voltammetry.The electro-oxidation behavior of formic acid was greatly influenced by the morphology and dispersion of Pt deposits on the Au nanoparticles.The electro-oxidation of formic acid occurred mainly in the high potential range(0.61.0 V vs SCE) when the Pt existed as a shell fully covering the Au particles in the Ptm^Au/C catalysts(m>0.2), which is similar to the electro-catalysis of a Pt/C catalyst.When the state of Pt deposits was varied from a mono-atomic Pt shell(m≈0.2) to very small flecks of Pt clusters or two-dimensional rafts(m<0.2) on the same Au particles,dramatic enhancement in the oxidation current of formic acid was observed in the low potential range(-0.2-0.6 V vs SCE).The massspecific activity of Pt at peak potential(0.38 V) in a Pt0.05^Au/C catalyst with a 100% Pt dispersion(EAS= 236 m2/g-Pt) was as high as about 40 times that of traditional Pt/C catalysts with about 30% Pt dispersion(EAS=74 m2/gPt).These results demonstrate that the catalytic activity of Ptm^Au/C catalysts for formic acid electro-oxidation could be dramatically enhanced by decreasing the size of Pt entities or increasing the Pt dispersion on Au particles.On varying the concentration of formic acid,we observed distinct volcano curves by correlating the electro-oxidation current with the concentration of formic acid for both Ptm^Au/C and Pt/C catalysts.Therefore,the determination of an appropriate concentration window for formic acid can be a key factor to the power densities of direct formic acid fuel cells using Pt-based electrocatalysts.更多还原