硫酸(氢)根吸附层对Pd(111)电极上甲酸氧化反应的影响研究

本文使用循环伏安法和电势阶跃法分别研究了添加和不添加Na₂SO₄的0.1 mol/LH₂SO₄+0.1 mol/LHCOOH溶液中Pd(111)电极上甲酸氧化反应(FAO)的动力学行为，并与同样条件下0.1 mol/LHClO₄中的动力学行为进行比较. 加入0.05 mol/L或者0.1 mol/LNa₂O₄后，在相同的电位下负向扫描的FAO电流比正向扫描的显著减小. 本文推测在(SO₄^*_ad)_m+(H₂O)_n-H₃O⁺]或(SO₄^*_ad)_m+Na⁺(H₂O)_n-H₃O⁺]吸附层相转变电势以正的电位, 这个吸附层的结构可能随着电位的增加或Na₂SO₄的加入变得更加致密和稳定. 因此，破坏或者脱附致密的硫酸(氢)根吸附层变得更加困难，使得FAO 动力学在较高电位和随后的负扫电位受到明显的抑制.

Effect of Sulfate Adlayer on Formic Acid Oxidation on Pd(111) Electrode

The kinetics of formic acid oxidation (FAO) on Pd(111) in 0.1 mol/L H₂SO₄+0.1 mol/LHCOOH with and without addition of Na₂SO₄ is studied using cyclic voltammetry and potential step method, which is compared with that in 0.1 mol/L HClO₄. It is found that adsorbed sulfate has significant inhibition effect on FAO kinetics. After addition of 0.05 mol/L or 0.1 mol/L Na₂SO₄, FAO current in the negative-going scan is found to be significantly smaller than that at the same potential in the positive-going scan. We speculate that at potentials positive of the phase transition potential for the (SO₄^*_ad)_m+(H₂O)_n-H₃O⁺] or (SO₄^*_ad)_m+Na⁺(H₂O)_n-H₃O⁺] adlayer, the adlayer structure probably becomes denser and more stable with the increase of potential or with the addition of Na₂SO₄. The formation of connected adlayer network greatly enhance the stability of the adlayer, and the insertion of positive-charged H⁺ or Na⁺ into the adlayer network further reduces the electrostatic repulsion between partially charged sulfates. As a result, the destruction/desorption of compact sulfate adlayer becomes more difficult, which leaves much less free sites on the surface for FAO, and thus FAO kinetics at higher potentials and in the subsequent negative-going potential scan is significantly inhibited.