本研究以薄膜電極方法探討鈀黑(Pd-black)觸媒在酸性電解質溶液中電催化甲酸氧化的反應動力學。利用循環伏安法多次掃描得知Pd-black 電極的氫吸/脫附電荷量會隨著掃描圈數的增加而漸漸減少，這是由於Pd 觸媒表面化學吸附H+離子所致。再者，氫吸附peak I (-0.125V vs. Ag/AgCl)對氫的化學吸附活性明顯高於氫吸附peak II (0.043Vvs. Ag/AgCl)，這些現象將降低Pd-black 觸媒在酸性電解質溶液中的電化學活化面積，並導致觸媒活性與壽命的減退。利用線性掃描伏安法所求得甲酸分子在Nafion 覆蓋Pd-black 薄膜電極中的擴散係數為1.3×10-6 cm2s-1。與以計時安培法並藉由Cottrell 方程式所求得的擴散係數值具有相同的數量級(10-6)。所求得擴散係數值上的些微差異可歸因於實驗誤差。
In the work, the reaction kinetics of electrocatalytic formic acid oxidation at Pd-black catalyst in acid electrolyte was investigated using a thin-film rotating disk electrode configuration. The cyclic voltammetric results showed that the charge for H-adsorption/desorption of the electrode was gradually reduced with the prolonged potential cycling. This could be attributed that the Pd catalyst surface was chemically absorbed by H+ ions.Moreover, H-adsorption peak I (-0.125V vs. Ag/AgCl) significantly exhibited higher chemsorption activity than that for H-adsorption peak II (0.043V vs. Ag/AgCl). This effect would reduce the electrochemical active surface and in turn caused a decrease in the overall catalytic activity of Pd-black. The diffusion coefficient of formic acid at the Nafion-covered Pt-black electrode was determined to be 1.3×10-6 cm2s-1 by the linear sweep voltammetry.Compared to the data obtained by chronoamperometry using the Cottrell equation, the values
of the diffusion coefficient were with the same order of magnitude. The small differences by these two methods were due to the experimental errors.
