Theoretical descriptors differentiate the catalytic activity of materials for the oxygen evolution reaction by the strength of oxygen binding in the reactive intermediate created upon electron transfer. Recently, time-resolved spectroscopy of a photo-electrochemically driven oxygen evolution reaction followed the vibrational and optical spectra of this intermediate, denoted M-OH^*. However, these inherently kinetic experiments have not been connected to the relevant thermodynamic quantities. Here we discover that picosecond optical spectra of the Ti-OH^* population on lightly doped SrTiO₃ are ordered by the surface hydroxylation. A Langmuir isotherm as a function of pH extracts an effective equilibrium constant relatable to the free energy difference of the first oxygen evolution reaction step. Thus, time-resolved spectroscopy of the catalytic surface reveals both kinetic and energetic information of elementary reaction steps, which provides a critical new connection between theory and experiment by which to tailor the pathway of water oxidation and other surface reactions.

理论描述符通过电子转移时产生的反应中间体中的氧结合强度来区分材料对析氧反应的催化活性。最近，光电化学驱动的析氧反应的时间分辨光谱遵循该中间体的振动和光谱，表示为 M-OH ^*。然而，这些固有的动力学实验尚未与相关的热力学量联系起来。在这里，我们发现轻掺杂 SrTiO _{3上 Ti-OH} ^*群的皮秒光谱由表面羟基化排序。作为 pH 函数的朗缪尔等温线提取了与第一个析氧反应步骤的自由能差相关的有效平衡常数。因此，催化表面的时间分辨光谱揭示了基本反应步骤的动力学和能量信息，这在理论和实验之间提供了一个重要的新联系，通过它来定制水氧化和其他表面反应的途径。