Weber Tim, Vonk Vedran, Abb Marcel J S, Evertsson Jonas, Sandroni Martina, Drnec Jakub, Stierle Andreas, Lundgren Edvin, Over Herbert
Institute of Physical Chemistry, Justus Liebig University, Heinrich-Buff-Ring 17, 35392 Giessen, Germany.
Center for Materials Research, Justus Liebig University, Heinrich-Buff-Ring 16, 35392 Giessen, Germany.
J Phys Chem Lett. 2020 Nov 5;11(21):9057-9062. doi: 10.1021/acs.jpclett.0c02730. Epub 2020 Oct 12.
Down to a cathodic potentials of -1.20 V versus the reversible hydrogen electrode, the structure of IrO(110) electrodes supported by TiO(110) is found to be stable by in situ synchrotron-based X-ray diffraction. Such high cathodic potentials should lead to reduction to metallic Ir (Pourbaix diagram). From the IrO lattice parameters, determined during cathodic polarization in a HSO electrolyte solution (pH 0.4), it is estimated that the unit cell volume increases by 1% due likely to proton incorporation, which is supported by the lack of significant swelling of the IrO(110) film derived from X-ray reflectivity experiments. Ex situ X-ray photoelectron spectroscopy suggests that protons are incorporated into the IrO(110) lattice below -1.0 V, although Ir remains exclusively in the IV+ oxidation state down to -1.20 V. Obviously, further hydrogenation of the lattice oxygen of IrO(110) toward water is suppressed for kinetic reasons and hints at a rate-determining chemical step that cannot be controlled by the electrode potential.
通过基于同步加速器的原位X射线衍射发现，相对于可逆氢电极，当阴极电位降至-1.20 V时，由TiO(110)支撑的IrO(110)电极结构是稳定的。如此高的阴极电位应会导致还原为金属铱（Pourbaix图）。根据在HSO电解质溶液（pH 0.4）中阴极极化期间测定的IrO晶格参数，估计晶胞体积可能因质子掺入而增加1%，这得到了X射线反射率实验中IrO(110)薄膜没有明显膨胀的支持。非原位X射线光电子能谱表明，质子在低于-1.0 V时掺入IrO(110)晶格，尽管直到-1.20 V铱仍仅处于IV+氧化态。显然，由于动力学原因，IrO(110)晶格氧向水的进一步氢化受到抑制，这暗示了一个速率决定化学步骤，该步骤不受电极电位控制。
