Hidden Potential of Halide Perovskites in Photo‐Electrocatalytic Syngas Production: Triumph or Trial?

ABSTRACT Halide perovskites have been revolutionizing every branch where they were introduced, including solar cells, light‐emitting devices, transistors, sensors, and catalysis, and have emerged as true wonder materials over the past decade. Herein, we report first demonstration of halide perovskite‐based photocathode for photoelectrocatalytic CO 2 reduction to syngas. A vacancy‐ordered Cs 2 PtI 6 halide perovskite exhibits exceptional stability and activity, overcoming the intrinsic limitations of conventional halide perovskites under electrochemical conditions. Under light irradiation, Cs 2 PtI 6 enables efficient CO 2 reduction with significantly enhanced reaction kinetics. CO 2 reduction to CO accompanied by H 2 evolution was successfully achieved, delivering maximum Faradaic efficiency (FE) of 96.7% ± 1.6% at −0.46 V vs RHE for syngas production. Notably, Cs 2 PtI 6 photocathode enables a tunable CO/H 2 ratio that can be controlled from 1.1 to 2.2 by varying applied potential. The FE of 62.6% for CO production was attained at exceptionally low potential of −0.06 V vs RHE. Remarkably, Cs 2 PtI 6 delivered ultrahigh current density exceeding −500 mA cm −2 at −0.9 V vs RHE. The combined in situ DRIFTS and DFT results identify the reaction intermediates and provide mechanistic insights into CO 2 reduction over Cs 2 PtI 6 . This work establishes halide perovskites as a new class of robust photoelectrocatalysts for efficient and tunable syngas production.