Hydrothermal Synthesis and Electro-Activity of Titanium-Supported Silver Electrodes
Abstract:
Three novel titanium-supported silver electrodes (Ag/Ti-N2H4,Ag/Ti-PEG,Ag/Ti-PEG-EDTA) were fabricated by a hydrothermal process using AgNO3,PEG,hydrazine,and EDTA as reaction materials. SEM and EDS images showed that a stable silver particle layer formed on the surface of titanium,the surface of three electrodes had different structural features. Ag/Ti-N2H4 electrode formed a 1 μm silver spherical particle layer,Ag/Ti-PEG formed a 400600 nm silver spherical particle layer,and Ag/Ti-PEG-EDTA electrode formed a 200300 nm silver spherical particle layer with a three-dimensional network structure. Oxidation of hydrazine on the electrodes in 1 mol·L-1 NaOH solution was studied with cyclic voltammograms (CV). The results showed that the three kinds of electrodes all had electro-catalytic activity for hydrazine oxidation. The onset potentials of hydrazine oxidation on Ag/Ti-PEG-EDTA,Ag/Ti-N2H4 and Ag/Ti-PEG were -0.6,-0.6 and -0.7 V,respectively,all were less than that on the polycrystalline silver electrode (-0.35 V). At -0.36 V,the oxidation peak current densities of hydrazine in 1.0 mol·L-1NaOH+20 mmol·L-1N2H4 solution on the polycrystalline silver,Ag/Ti-N2H4,Ag/Ti-PEG-EDTA and Ag/Ti-PEG electrodes were 2.5,33,42 and 51 mA·cm-2,respectively. The results showed that Ag/Ti-PEG-EDTA and Ag/Ti-PEG electrodes had significantly higher electro-activity for the hydrazine oxidation. These novel electrodes would be the promising anodic materials which could be used in direct hydrazine fuel cells.
Alvarez-Ruiz等研究了肼在单晶铂表面和铂的氧化物表面的催化氧化
[7,8],在碱性溶液中,对肼在多晶铂表面的催化氧化也进行了研究,其氧化的起始电位为0.1 V vs.SHE(或-0.141 V vs.SCE)
[9],这表明肼在铂电极上的氧化要求比较高的过电位。Korinek等研究了水合肼在银电极表面的催化氧化
[10],最近Gao等也研究了肼在银碳纳米管(Ag/CNT)和银多孔碳纳米管(Ag/MWNT)上的催化氧化
[11,12],在K2SO4溶液中,其氧化的起始电位为-0.3 V vs.SCE,肼在金属金
[13]、镍
[14]和汞
[15]表面的氧化也有一些研究。
Fig.1 Scanning electron micrographs(SEM,(a),(b),(c))of the sample Ag/Ti-N2H4,Ag/Ti-PEG,Ag/Ti-PEG-EDTA and en-ergy disperse spectroscopy(EDS,(d))of the sample Ag/Ti-PEG-EDTA
Fig.2 CV curves of the Ag,Ag/Ti-N2H4,Ag/Ti-PEG,Ag/Ti-PEG-EDTA electrodes from-1.2~1.0 V at the scan rate of 100 mV s-1 in 1.0 mol L-1NaOHsolution
在0.5 V左右处的氧化峰为银的高价态的氧化峰,
从图2看出,在Ag/Ti-PEG电极和Ag/TiN2H4电极上,银的高价氧化峰的电流密度分别为55.6和29.8 mA cm-2,而在Ag/Ti-PEG-EDTA电极上的电流密度高达202.9 mA cm-2,是Ag/TiPEG电极和Ag/Ti-N2H4电极的3倍和6倍还多。我们由此推断这可能是因为在Ag/Ti-PEG-EDTA电极表面上分散了大量的金属银纳米颗粒,增大了其比表面积,从而导致电流密度的剧增,这也与其SEM图像所表现出的网络状多孔结构是一致的。
Fig.3 CV curves of the Ag,Ag/Ti-N2H4,Ag/Ti-PEG,Ag/Ti-PEG-EDTA electrodes from-1.2~1.0 V at the scan rate of 100 mV s-1 in 1.0 mol L-1 NaOH+20mmol L-1N2H4 H2O solution