Stand-alone photoconversion of carbon dioxide on copper oxide wire arrays powered by tungsten trioxide/dye-sensitized solar cell dual absorbers

• Stand-alone photoelectrochemical cell for CO2 conversion was designed.
• WO3/DSSC and copper oxide (CuxO) wire arrays were coupled as a dual-absorber photoanode and cathode, respectively.
• In the dual-absorber cell, the long-wave band passed through the semitransparent WO3 film is absorbed by DSSC.
• The primary CO2 conversion product is CO, with an energy efficiency of ~2.5% (overall efficiency ~3.45%).
• Neither CO2 conversion product nor H2 is produced by the single-absorber system.

A photoelectrochemical (PEC) cell composed of a WO3/dye-sensitized solar cell (WO3/DSSC) and copper oxide (CuxO, where x=1 and 2) wire arrays as a dual-absorber photoanode and cathode, respectively, is demonstrated as a stand-alone, durable device for CO2 photoconversion. The CuxO wire arrays, which have high surface-to-volume ratios, exhibit promising electrocatalytic activity for CO2 conversion to CO at Faradaic efficiencies of ~80% and ~60% at E=−0.2 and −0.4 V vs. RHE, respectively, and H2 production is minimized at a Faradaic efficiency <~20% in the potential range between −0.2 and −1.0 V vs. RHE. The single-absorber cell of a WO3 photoanode and CuxO wire array cathode couple (WO3-CuxO) requires a minimum overpotential of ~0.7 V to drive CO2 conversion. For stand-alone CO2 conversion, a DSSC is coupled to the WO3-CuxO system. In the dual-absorber cell (WO3/DSSC-CuxO), the long-wave band (λ >ca. 450 nm) passed through the semitransparent WO3 film is absorbed by the dye-sensitized TiO2 electrode of the DSSC. The WO3/DSSC-CuxO shows a potential gain of ~0.7 V and is able to successfully drive CO2 conversion on CuxO and simultaneously oxidize water on WO3 without an external power supply. In this stand-alone system, the primary CO2 conversion product is CO, with a solar-to-chemical energy efficiency of ~2.5%; H2 and formate are obtained with energy efficiencies of 0.7% and 0.25%, respectively, in 5 h (overall efficiency ~3.45%). Neither CO2 conversion product nor H2 is found using the single-absorber system.

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