Insights into the development of Cu-based photocathodes for carbon dioxide (CO2) conversion

The ever-growing over-consumption of fossil fuels and the accompanying massive emissions of CO2 have caused a severe energy crisis and environmental issues. Photoelectrochemical (PEC) reduction of CO2 that can combine and optimize the merits of both photocatalysis and electrocatalysis has been considered as an attractive prospect for addressing the two problems. Herein, photocathode materials are cores of PEC CO2 reduction. Among various photocathodes, Cu-based photocathodes attract much attention due to their low toxicity, low cost, earth-abundant properties, appropriate range of bandgap values and favorable band edges for CO2 reduction. More to the point, Cu-based photocathodes possess unique advantages for hydrocarbon production such as CO, HCOOH, CH4 or, more importantly, C-2 products (like C2H4, C2H5OH and C2H6) compared with other metallic-based photoelectrodes. An insight into the relationships between the properties and functions of photocathodes plays a vital role in the field of PEC CO2 reduction. This review presents the development of Cu-based photocathode materials and discusses future research directions. The photocathode systems mainly include Cu-based oxides, Cu-based chalcogenides and Cu-based electrocatalyst coupled photocathodes. Subsequently, the existing major advantages and disadvantages of each system are also discussed. In conclusion, combining our analyses of the reported photocathodes, we will offer future challenges for the rational design of photoelectrodes. Overall, this review will present a significant overview of Cu-based photocathodes for PEC reduction of CO2.