Highly Efficient Photoelectrochemical Water Oxidation Using Cs2AgMCl6(M = In,Bi,Sb ) Halide Double Perovskites

Abstract

In this work, stable ${\mathrm{Cs}}_{2}\mathrm{Ag}M{\mathrm{Cl}}_{6}(M$ = $\mathrm{Bi},\mathrm{In},\mathrm{Sb}$) double perovskite materials are successfully employed as photoanodes for solar water oxidation. These materials show an extraordinary oxidative stability, where ${\mathrm{Cs}}_{2}{\mathrm{Ag}\mathrm{In}\mathrm{Cl}}_{6}$ and ${\mathrm{Cs}}_{2}{\mathrm{Ag}\mathrm{Bi}\mathrm{Cl}}_{6}$ are stable between 0 and 1.2 V (vs $\mathrm{Ag}\text{\ensuremath{-}}\mathrm{Ag}\mathrm{Cl}$) and ${\mathrm{Cs}}_{2}{\mathrm{Ag}\mathrm{Sb}\mathrm{Cl}}_{6}$ between 0 and 0.75 V (vs $\mathrm{Ag}\text{\ensuremath{-}}\mathrm{Ag}\mathrm{Cl}$) over 100 cycles of electrochemical cycling. This enables us to employ these materials for photoelectrochemical (PEC) water oxidation in ${\mathrm{CH}}_{3}\mathrm{CN}$ and ${\mathrm{H}}_{2}\mathrm{O}$, with and without ${\mathrm{Ir}\mathrm{O}}_{x}$ cocatalyst. All three materials show PEC activity, with ${\mathrm{Cs}}_{2}{\mathrm{Ag}\mathrm{In}\mathrm{Cl}}_{6}$ showing the highest performance. At 1.23 V (vs a reversible hydrogen electrode), a photocurrent density of 0.5 mA ${\mathrm{cm}}^{\ensuremath{-}2}$ is observed, and with an applied overpotential of 600 mV, the photocurrent increases to about 0.75 mA ${\mathrm{cm}}^{\ensuremath{-}2}$. From the band gap of ${\mathrm{Cs}}_{2}{\mathrm{Ag}\mathrm{In}\mathrm{Cl}}_{6}$, the estimated theoretical maximum current is around 0.82 mA ${\mathrm{cm}}^{\ensuremath{-}2}$. So, ${\mathrm{Cs}}_{2}{\mathrm{Ag}\mathrm{In}\mathrm{Cl}}_{6}$-coated ${\mathrm{Ir}\mathrm{O}}_{x}$ gives nearly 60% and about 90% of the theoretical maximum photocurrent at zero bias and at an applied overpotential, respectively. The device is shown to be stable and reproducibility is confirmed.