Carbon Encapsulation of Organic–Inorganic Hybrid Perovskite toward Efficient and Stable Photo‐Electrochemical Carbon Dioxide Reduction

Photo‐electrochemical (PEC) carbon dioxide reduction to chemicals or fuels has been regarded as an attractive strategy that can close the anthropogenic carbon cycle. However, identifying a PEC system capable of driving efficient and durable CO2 conversion remains a critical challenge. Herein, the fabrication of a sandwich‐like organic–inorganic hybrid perovskite‐based photocathode with carbon encapsulation for PEC CO2 reduction is reported. The carbon encapsulation not only affords protection to the perovskite, but also allows for efficient conductance of photogenerated electrons. When decorated with a cobalt phthalocyanine molecular catalyst, the photocathode shows an onset potential at 0.58 V versus reversible hydrogen electrode (RHE) and a high photocurrent density of −15.5 mA cm−2 at −0.11 V versus RHE in CO2‐saturated 0.5 m KHCO3 under AM 1.5G illumination (100 mW cm−2), which represents state‐of‐the‐art performance in this field. Moreover, the photocathode remains stable during a continuous reaction that lasted for 25 h. Unbiased PEC CO2 reduction is further realized by integrating the photocathode with an amorphous Si photoanode in tandem, delivering a solar‐to‐CO energy conversion efficiency of 3.34% and a total solar‐to‐fuel energy conversion efficiency of 3.85%. A carbon‐encapsulated (Cs0.15FA0.85)Pb(I0.9Br0.1)3 photocathode with a sandwich‐like structure is prepared and demonstrates state‐of‐the‐art performance for photo‐electrochemical (PEC) CO2 reduction among organic–inorganic hybrid perovskite‐based PEC devices. A tandem device consisting of this photocathode and a Si photoanode further realizes unbiased PEC CO2 reduction with an outstanding solar‐to‐CO energy conversion efficiency of 3.34%.