The consistent fabrication of high performance α-Fe₂O₃ photoanodes for the oxygen evolution reaction remains a challenge. We work towards resolving this issue by developing in situ variable temperature Raman spectroscopy as a means to better understand the formation of α-Fe₂O₃, using the conversion of γ-FeOOH to α-Fe₂O₃ under varied gaseous environments as a model case. The sensitivity of Raman spectroscopy to structural changes provides mechanistic insights that are not readily available in more conventional approaches, such as thermal gravimetric analysis and differential scanning calorimetry. The Raman spectra are combined with conventional thermal analyses to interpret the photoelectrocatalytic performance of a series of α-Fe₂O₃ photoanodes prepared by systematic variation of a three-stage annealing protocol. The combined results suggest that protohematite, a form of α-Fe₂O₃ where trapped hydroxyl ligands are balanced by Fe(III) vacancies, forms between 200 C and 400 C in a reaction environment-dependent fashion. This protohematite is shown to be remarkably persistent once formed, degrading photoelectrocatalytic performance. This research advances understanding of the γ-FeOOH to α-Fe₂O₃ structural transformation, illustrates a powerful method to study solid state phase transitions, and provides guidance for the synthesis of high quality α-Fe₂O₃ from a convenient precursor.

一致地制造用于析氧反应的高性能α -Fe ₂ O _{3 光}阳极仍然是一个挑战。我们致力于通过开发原位变温拉曼光谱来解决这个问题，以此来更好地了解α -Fe ₂ O ₃的形成，利用γ -FeOOH 到α -Fe ₂ O ₃的转化在各种气体环境下作为模型案例。拉曼光谱对结构变化的敏感性提供了在更传统的方法（例如热重分析和差示扫描量热法）中不容易获得的机械见解。拉曼光谱与常规热分析相结合，以解释通过三级退火方案的系统变化制备的一系列α -Fe ₂ O _{3 光}阳极的光电催化性能。综合结果表明原赤铁矿，一种α -Fe ₂ O ₃其中捕获的羟基配体由 Fe(III) 空位平衡，在 200 C 和 400 C 之间以依赖于反应环境的方式形成。这种原赤铁矿一旦形成就表现出显着的持久性，从而降低了光电催化性能。这项研究促进了对γ -FeOOH 到α -Fe ₂ O ₃结构转变的理解，说明了研究固态相变的强大方法，并为从方便的前体合成高质量α -Fe ₂ O ₃提供了指导。