Excessive carbon dioxide (CO₂) emission has caused problems associated with environmental pollution and climate deterioration. As a consequence, the selective conversion of CO₂ into liquid fuels by artificial photosynthesis has gained increasing attention. However, the rational design of photocathode to achieve selective CO₂ photoelectroreduction is challenging. Here, we sensitized cuprous oxide (p-nCu₂O) loaded on hydroxyl iron oxide (FeOOH) with cobalt-doped cadmium sulfide (Co:CdS) quantum dots to prepare a novel photocathode FeOOH/p-nCu₂O/Co:CdS by sequential electrodeposition and chemical bath deposition. The composite photocathode exhibited a larger photovoltage, which is 1.9 times higher than the pristine counterpart, and was efficient for CO₂ reduction to produce formic acid with high selectivity of up to 82.9% (Faradaic efficiency). Theoretical calculations revealed that the photocathode out-layer Co:CdS quantum dots had increased binding energy toward the key intermediate *OOCH through additional hybridization orbitals to exclusively favor the formation of formic acid. An impurity energy level was revealed to form by doping Co to the CdS-containing composite, which could reduce the photocathode band gap with improved absorption toward visible light, thus remarkably increasing the photoelectrochemical properties. This is the first work undertaking the energy band structure optimization of the photocathode enabled by elemental doping to improve its photoelectrocatalytic performance.

过量的二氧化碳(CO ₂ )排放引起了与环境污染和气候恶化相关的问题。因此，通过人工光合作用选择性地将CO ₂转化为液体燃料受到越来越多的关注。然而，合理设计光电阴极以实现选择性CO ₂光电还原是具有挑战性的。在这里，我们用钴掺杂硫化镉（Co:CdS）量子点敏化负载在羟基氧化铁（FeOOH）上的氧化亚铜（p-nCu _{2 O），制备了新型光电阴极FeOOH/p-nCu 2} O/Co:CdS通过连续电沉积和化学浴沉积。复合光电阴极表现出更大的光电压，比原始光电阴极高1.9倍，并且能够有效地还原CO ₂生成甲酸，选择性高达82.9%（法拉第效率）。理论计算表明，光电阴极外层 Co:CdS 量子点通过额外的杂化轨道增加了对关键中间体 *OOCH 的结合能，专门有利于甲酸的形成。研究表明，通过将Co掺杂到含CdS复合材料中可以形成杂质能级，这可以减小光电阴极带隙，提高对可见光的吸收，从而显着提高光电化学性能。这是第一个通过元素掺杂优化光电阴极能带结构以提高其光电催化性能的工作。