Hou Jiajie, Chang Xiaoxia, Li Jing, Xu Bingjun, Lu Qi
State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing100084, China.
College of Chemistry and Molecular Engineering, Peking University, Beijing100871, China.
J Am Chem Soc. 2022 Dec 7;144(48):22202-22211. doi: 10.1021/jacs.2c09956. Epub 2022 Nov 20.
The absolute coverage of CO has been a missing piece in the mechanistic puzzle of the CO reduction reaction (CORR) on Cu. For the first time, we revealed the upper bound of the CO coverage under electrocatalytic conditions to be 0.05 monolayer at atmospheric pressure and the saturation CO coverage to be ∼0.25 monolayer by conducting surface enhanced infrared spectroscopy at CO pressures up to 60 barg in a custom-designed spectroelectrochemical cell. CORR activities on Cu were also determined in the same pressure range. Calculated reaction orders of C products with respect to adsorbed CO are substantially less than unity, clearly indicating that the coupling of adsorbed CO is not the rate-determining step leading to multicarbon products. The increase in CO coverage can reduce the C affinity on the Cu surface and favor the selectivity towards oxygenates, especially acetate, over ethylene. Uncommon products, including ethane, glycolaldehyde, and ethylene glycol, were detected in appreciable amounts, likely due to a new C-C coupling mechanism taking place at elevated CO pressures.
一氧化碳（CO）的绝对覆盖度一直是铜上CO还原反应（CORR）机理难题中缺失的一环。我们首次通过在定制设计的光谱电化学池中，在高达60巴表压的CO压力下进行表面增强红外光谱研究，揭示了在大气压力下电催化条件下CO覆盖度的上限为0.05单层，饱和CO覆盖度约为0.25单层。同时，也在相同压力范围内测定了铜上的CORR活性。计算得出的C产物相对于吸附CO的反应级数远小于1，这清楚地表明吸附CO的偶联不是导致多碳产物的速率决定步骤。CO覆盖度的增加会降低铜表面对C的亲和力，并有利于生成含氧化合物，尤其是醋酸盐，而不是乙烯。还检测到了大量不常见的产物，包括乙烷、乙醇醛和乙二醇，这可能是由于在较高CO压力下发生了新的C-C偶联机制。
