枝状银-钯复合材料的制备及电催化氧化乙醇性能研究

Preparation of Silver-Palladium Fractal Composite for Ethanol Electro-Oxidation in Alkaline Media

通过电沉积法在碳纸表面制备了枝状银微纳结构(Ag-Fr),再利用电置换反应(GRR),在枝状银表面置换上一层钯元素,形成枝状银-钯复合材料(Ag_xPd_y-Fr)。所得复合材料的形貌和成分经过粉末X射线衍射(XRD)、扫描电镜(SEM)、电感耦合等离子体原子发射光谱(ICPOES)等手段表征。利用电化学方法研究了枝状银-钯复合材料Ag_xPd_y-Fr在碱性条件下对乙醇的电催化氧化活性,并与与商业Pd/C催化剂进行了比较。通过对比,在制备的几种催化剂中,Ag_(94)Pd_6-Fr在碱性条件下对乙醇的电催化氧化活性最高。由电催化氧化乙醇(EOR)的循环伏安(CVs)研究可知,乙醇在Ag_(94)Pd_6-Fr上的正向扫描氧化峰电流密度最高,为~33 m A·cm^(-2),约为Pd/C上的11倍,且起始峰电位约比Pd/C上的低0.08 V。乙醇在Ag_(91)Pd_9-Fr和Ag_(87)Pd_(13)-Fr上的正向扫描氧化峰电流密度分别为Pd/C上的9.3倍和5.4倍,起始峰电位分别比Pd/C上的低0.06和0.01 V。当置换时间超过2 h后,枝状结构的细微结构消失,整个结构间的空隙变小,比表面积减小,加上表面AgCl沉淀的生成和覆盖,虽然此时枝状复合材料的钯含量增,但电催化活性较低。

Silver-palladium fractal-like composites （AgxPdy-Fr） were facilely prepared via a galvanic replacement reaction （GRR） with electrodeposited fractal silver structure （Ag-Fr） on carbon paper as sacrificed templates. The composition and morphology of the as-fabricated composites were characterized by X-ray diffraction （ XRD）, scanning electron microscopy （SEM） and inductively coupled plasma optical emission spectroscopy （ICP-OES）, etc. The catalytic activity and stability of the as-prepared Ag^Pd^-Fr composites to- ward electro-oxidation of ethanol in alkaline media were investigated through electrochemistry and compared with commercial Pd/C cat- alyst. By comparison, Ag94Pd6-Fr showed superior catalytic activity towards electro-oxidation of ethanol in alkaline media than the other catalysts studied in this work. By evaluating the cyclic voltammograms （CVs） of ethanol electro-oxidation reaction （ EOR）, the EOR on Ag94Pd6-Fr showed the highest forward scan anodic peak current density of -33 mA cm-2, which was about 11 times higher than that on commercial Pd/C. Besides, the onset potential was about 0.08 V lower than that on Pd/C. The forward scan anodic peak cur- rent densities of EOR on Ag91Pd9-Fr and AgsTPd13-Fr were 9.3 and 5.4 times higher than that on Pd/C, respectively, while the onset potentials were 0.06 and 0.01 V lower than that on Pd/C. When the GRR time was longer than 2 h, the fine structure of the fractal disappeared which resulted in narrowed interspace and low surface area to volume ratio of the composites. Moreover, the AgC1 precipi- tates were produced and covered the surface of the composites during GRR. Therefore, although Pd loading increased with GRR time, the AgxPdy-Fr composites generated by long time GRR showed low electrocatalytic activity toward EOR.