A method comprising irradiating ultraviolet light on at least one solid composite electrode comprising at least one semiconductor material which is in contact with at least one liquid solution comprising carbon dioxide; wherein at least one proton source is also present in the electrode and/or in the liquid solution comprising carbon dioxide; wherein the irradiating step results in conversion of at least some carbon dioxide into at least one reaction product. High efficiency conversion of carbon dioxide to ethanol can be achieved. The liquid solution can be aqueous, the proton source can be hydroquinone, and the semiconductor material can be zinc sulfide. The solid composite electrode can be a working electrode and used in conjunction with a counter electrode in a photoelectrochemical system. The system can be operated in alternating closed and open circuit mode.