Photoelectrochemical Nitrogen Reduction: Activity, Selectivity and Stability of Cu-based Ternary Oxide Photocathodes

光电化学（PEC）N2固定是目前探索的可能途径，以收获太阳能碳中性氨生产。在这方面的追求，我们提出了一个紧密结合的实验和计算的努力，调查合理选择的一类三元铜基氧化物光电阴极，即CuFeO 2和CuBi 2 O 4的PEC氮还原反应（NRR）的活动和机制。这些材料提供合适的带隙用于捕获阳光，合适的带边位置用于N2固定，并且重要的是，p型导电性。密切相关的二元氧化物CuO和Cu 2 O已经表现出有希望的NRR活性。三元铜氧化物，然而，尚未探索这种反应。与二元化合物相比，这些三元铜氧化物具有在水性PEC操作条件下更稳定的明显优势。此外，它们提供了更大种类的具有双功能性潜力的表面位点。因此，三元铜基氧化物不仅是实现PEC NRR的理想候选者，而且与二元氧化物相比，它们也是研究异质表面位如何影响铜基氧化物光电阴极的活性、选择性和稳定性的理想模型体系。我们的项目旨在解决三个目标：1）建立组成-结构-活性关系，2）探测工作界面的化学变化; 3）阐明CuFeO_2和CuBi_2 O_4的PEC NRR机理。这些目标解决了硝基转化优先计划（SPP 2370）的三个核心领域中的两个，即“催化剂合成及其物理化学表征”和“反应机理的实验和理论研究”。在合成和PEC表征相纯铜基氧化物光电阴极之后，我们将联合收割机结合原子分辨显微镜和光谱学与理论研究来分析PEC NRR条件下的固体电解质界面。这种组合使我们能够直接比较宏观PEC性能与原子模拟。我们的实验技术包括操作溶解测量，以评估光电阴极的稳定性，操作傅里叶变换红外（FTIR）光谱探测固体电解质界面的中间体，和差分电化学质谱（DEMS）的反应产物的在线分析。在我们的理论方法中，我们将实现一个有效的方法来明确处理溶剂化环境。这种实现将使我们能够在密切模仿实验环境的条件下计算热化学NRR途径。在整个工作中，我们将实验与互补理论紧密结合，这将有助于我们确定PEC NRR的催化相关表面结构，并为相关反应途径提供新的见解。

Photoelectrochemical (PEC) N2 fixation is currently explored as possible route towards harvesting solar energy for carbon-neutral ammonia production. Within this quest, we propose a tightly integrated experimental and computational effort to investigate the activity and mechanism of the PEC nitrogen reduction reaction (NRR) on a rationally selected class of ternary Cu-based oxide photocathodes, namely CuFeO2 and CuBi2O4. These materials offer suitable band gaps for capturing sunlight, appropriate band edge positions for N2 fixation, and, importantly, p-type conductivity. The closely related binary oxides, CuO and Cu2O, have already exhibited promising NRR activity. The ternary Cu oxides, however, are yet to be explored for this reaction. Compared to the binaries, these ternary Cu oxides have the distinct advantage of being more stable under aqueous PEC operating conditions. In addition, they provide a larger variety of surface sites with potential for bifunctionality. Thus, ternary Cu-based oxides are not only promising candidates to realize the PEC NRR, but when compared to the binaries, they are also ideal model systems to study how heterogeneous surface sites influence the activity, selectivity, and stability of Cu-based oxide photocathodes.Our project is designed to address three objectives aimed at 1) establishing composition-structure-activity relationships, 2) probing chemical changes at working interfaces, and 3) elucidating the PEC NRR mechanism on CuFeO2 and CuBi2O4. These objectives tackle two of the three core areas of the Nitroconversion priority program (SPP 2370), namely “catalyst synthesis and their physicochemical characterization” and “experimental and theoretical investigation of reaction mechanisms.” Following the synthesis and PEC characterization of phase-pure Cu-based oxide photocathodes, we will combine atomically-resolved microscopy and spectroscopy with theoretical studies to analyze the solid-electrolyte interface under PEC NRR conditions. This combination allows us to directly compare macroscopic PEC properties with atomistic simulations. Our experimental techniques include operando dissolution measurements to evaluate the stability of photocathodes, operando Fourier-Transform Infrared (FTIR) spectroscopy to probe intermediates at solid-electrolyte interfaces, and Differential Electrochemical Mass Spectrometry (DEMS) for online analysis of reaction products. In our theoretical approach, we will implement an efficient method for the explicit treatment of solvation environments. This implementation will allow us to compute thermochemical NRR pathways under conditions closely mimicking experimental environments. Our tight integration of experiments with complementary theory throughout this work will help us to identify the catalytically relevant surface structures for PEC NRR and provide new insights into the associated reaction pathways.