1 research outputs found
Discovery of a Hybrid System for Photocatalytic CO<sub>2</sub> Reduction via Attachment of a Molecular Cobalt-Quaterpyridine Complex to a Crystalline Carbon Nitride
While recent reports have demonstrated the attachment
of molecular
catalysts to amorphous, graphitic carbon nitrides (g-CN) for light-driven
CO2 reduction, approaches to the utilization of crystalline
carbon nitrides have remained undiscovered. Herein, a functional hybrid
photocatalyst system has been found using a crystalline carbon nitride
semiconductor, poly(triazine imide) lithium chloride (PTI-LiCl), with
a surface-attached CoCl2(qpy-Ph-COOH) catalyst for CO2 reduction. The molecular catalyst attaches to PTI-LiCl at
concentrations from 0.10 to 4.30 wt % and exhibits ∼96% selectivity
for CO production in a CO2-saturated, aqueous 0.5 M KHCO3 solution. Optimal loadings were found to be within 0.42–1.04
wt % with rates between 1,400 and 1,550 μmol CO/g·h at
an irradiance of 172 mW/cm2 (λ = 390 nm) and apparent
quantum yields of ∼2%. This optimized loading is postulated
to represent a balance between maximal turnover frequency (TOF; 300+
h–1) and excess catalyst that can limit excited-electron
lifetimes, as probed via transient absorption spectroscopy. An increase
in the incident irradiance yields a concomitant increase in the TOFs
and CO rates only for the higher catalyst loadings, reaching up to
2,149 μmol CO/g·h with a more efficient use of the catalyst
surface capacity. The lower catalyst loadings, by comparison, already
function at maximal TOFs. Higher surface loadings are also found to
help mitigate deactivation of the molecular catalysts during extended
catalytic testing (>24 h) owing to the greater net surface capacity
for CO2 reduction, thus representing an effective strategy
to extend lifetime. The hybrid particles can be deposited onto an
FTO substrate to yield ∼60% Faradaic efficiency for photoelectrochemical
CO production at −1.2 V vs Ag/AgCl bias. In summary, these
results demonstrate the synergistic combination of a crystalline carbon
nitride with a molecular catalyst that achieves among the highest
known rates in carbon-nitride systems for the light-driven CO2 reduction to CO in aqueous solution with >95% selectivity