Description:
Single-crystal, n-type MoSe2 (Eg=1.4 eV) is shown to serve as a stable photoanode in an electrochemical cell employing a nonaqueous (CH3CN) solution of Cl2/Cl− as the redox active material. At 90 mW/cm2 input, 632.8-nm light can be converted to electricity with an efficiency of 5.9–7.5%. The photoanode reaction is 2Cl−→Cl2 and the cathode reaction is Cl2→2Cl−. The MoSe2 is qualitatively better than MoS2 (∼0.5% efficiency) which has a larger band gap (1.7 eV), but both materials are rugged in the nonaqueous solution, while both photocorrode in aqueous Cl− solutions. In H2O, the I3−/I− couple is excellent but in CH3CN it yields lower efficiency than the Cl2/Cl− couple. The stable Cl2/Cl− system provides evidence that a transparent, reversible, non-O2-sensitive redox couple can be useful in n-type semiconductor-based liquid-junction cells employing a direct band gap material having optimum solar response.