Cu2Sn
x
Ge1–x
S3 (CTGS) particles were synthesized via
a solid-state reaction and assessed, for the first time, as both photocatalysts
and photocathode materials for hydrogen evolution from water. Variations
in the crystal and electronic structure with the Sn/Ge ratio were
examined experimentally and theoretically. The incorporation of Ge
was found to negatively shift the conduction band minimum, such that
the bandgap energy could be tuned over the range 0.77–1.49
eV, and also increased the driving force for the photoexcited electrons
involved in hydrogen evolution. The effects of the Sn/Ge ratio and
of Cu deficiency on the photoelectrochemical performance of Cu2Sn
x
Ge1–x
S3 and Cu
y
Sn0.38Ge0.62S3 (1.86 < y <
2.1) based photocathodes were evaluated under simulated sunlight.
Both variations in the band-edge position and the presence of a secondary
impurity phase affected the performance, such that a particulate Cu1.9Sn0.38Ge0.62S3 photocathode
was the highest performing specimen. This cathode gave a half-cell
solar-to-hydrogen energy conversion efficiency of 0.56% at 0.18 V
vs a reversible hydrogen electrode (RHE) and an incident-photon-to-current
conversion efficiency of 18% in response to 550 nm monochromatic light
at 0 VRHE. More importantly, these CTGS particles also
demonstrated significant photocatalytic activity during hydrogen evolution
and were responsive to radiation up to 1500 nm, representing infrared
light. The chemical stability, lack of toxicity, and high activity
during hydrogen evolution of the present CTGS particles suggest that
they may be potential alternatives to visible/infrared light responsive
Cu–chalcogenide photocatalysts and photocathode materials such
as Cu(In,Ga)(S,Se)2 and Cu2ZnSnS4.
(ZnSe)0.85(CuIn0.7Ga0.3Se2)0.15 (ZnSe:CIGS) photocatalytic particles are a promising candidate material for photocathodes in sunlight-driven photoelectrochemical (PEC) hydrogen evolution systems responsive up to 800-850 nm. However, the ZnSe:CIGS particles used in prior...
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