Lyle Hanna, Singh Suryansh, Paolino Michael, Vinogradov Ilya, Cuk Tanja
Renewable and Sustainable Energy Institute (RASEI), University of Colorado, Boulder, 80303, USA.
Materials Science and Engineering Program, University of Colorado, Boulder, 80303, USA.
Phys Chem Chem Phys. 2021 Nov 17;23(44):24984-25002. doi: 10.1039/d1cp01760h.
The conversion of diffusive forms of energy (electrical and light) into short, compact chemical bonds by catalytic reactions regularly involves moving a carrier from an environment that favors delocalization to one that favors localization. While delocalization lowers the energy of the carrier through its kinetic energy, localization creates a polarization around the carrier that traps it in a potential energy minimum. The trapped carrier and its local distortion-termed a polaron in solids-can play a role as a highly reactive intermediate within energy-storing catalytic reactions but is rarely discussed as such. Here, we present this perspective of the polaron as a catalytic intermediate through recent and time-resolved spectroscopic investigations of photo-triggered electrochemical reactions at material surfaces. The focus is on hole-trapping at metal-oxygen bonds, denoted M-OH*, in the context of the oxygen evolution reaction (OER) from water. The potential energy surface for the hole-polaron defines the structural distortions from the periodic lattice and the resulting "active" site of catalysis. This perspective will highlight how current and future time-resolved, multi-modal probes can use spectroscopic signatures of M-OH* polarons to obtain kinetic and structural information on the individual reaction steps of OER. A particular motivation is to provide the background needed for eventually relating this information to relevant catalytic descriptors by free energies. Finally, the formation of the O-O chemical bond from the consumption of M-OH*, required to release O and store energy in H, will be discussed as the next target for experimental investigations.
通过催化反应将扩散形式的能量（电能和光能）转化为短而紧密的化学键，通常涉及将载体从有利于离域的环境转移到有利于局域化的环境。虽然离域通过载体的动能降低了其能量，但局域化在载体周围产生了极化，将其捕获在势能最小值处。被捕获的载体及其局部畸变——在固体中称为极化子——在储能催化反应中可以作为高反应活性中间体发挥作用，但很少有人这样讨论。在这里，我们通过对材料表面光触发电化学反应的最新和时间分辨光谱研究，提出了极化子作为催化中间体的这一观点。重点是在水的析氧反应（OER）背景下，金属 - 氧键（表示为M - OH*）处的空穴捕获。空穴 - 极化子的势能面定义了与周期性晶格的结构畸变以及由此产生的催化“活性”位点。这一观点将突出当前和未来的时间分辨多模态探针如何利用M - OH极化子的光谱特征来获取OER各个反应步骤的动力学和结构信息。一个特别的动机是提供最终将这些信息与基于自由能的相关催化描述符联系起来所需的背景知识。最后，将讨论从M - OH的消耗形成O - O化学键以释放O并在H中储存能量，这将作为实验研究的下一个目标。
