Multi-layered photocathodes based on Cu₂ZnSnSe₄ absorber and MoS₂ catalyst for the hydrogen evolution reaction
2019
Grau, Sergi | Giraldo, Sergio | Saucedo, Edgardo | Morante, J. R. (Joan Ramón) | Llobet, Antoni | Gimbert-Suriñach, Carolina
A multilayered p-type photoabsorber based on kesterite Cu₂ZnSnSe₄ has been functionalized with inexpensive and easily scalable amorphous MoS₂ electrocatalyst by cathodic photoelectrodeposition. The resulting photocathodes with a final composition of Mo/MoSe₂/Cu₂ZnSnSe₄/CdS/ZnO/ITO/MoS₂ (where ITO = indium tin oxide) feature one of the highest hydrogen evolution catalytic current densities reported to date at a potential E = 0 V vs. RHE (−18 mA cm⁻² in pH 2) under 1 sun illumination. A comparison of the performance of the photoelectrode with an analogous dark electrode with composition ITO/MoS₂ allows us to estimate a photovoltage of 430 mV, which is very close to the working voltage of an equivalent photovoltaic cell with open circuit voltage VOC = 464 mV. The photoelectrodes show sustained activity at −10 mA cm⁻² above the thermodynamic potential of the H⁺/H₂ redox couple (E = +86 mV vs. RHE in pH 2) for 1 hour without any loss of activity. Prolonged reaction times up to 4 hours show no degradation of the photoabsorber multilayered architecture but a decrease in the thickness of the MoS₂ electrocatalytic film due to the mechanical stress caused by the hydrogen bubbles forming on the surface of the electrode. The MoS₂ layer is key not only to catalyze the catalytic reaction but also to protect the photoabsorber from the corrosive electrolyte solution. The adhesion of the MoS₂ electrocatalytic film on the ITO top layer is critical for the stability during hydrogen evolution catalysis.
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