Dual-Functional Atomic Layer Graphene Enable Bias-Free Photoelectrochemical Iodide Oxidation Reaction for Seawater Splitting
Yung-Hung Huang# , Po-Hsien Wu# , Yang-Sheng Lu# , Yin-Cheng Lin, Chih-Ying Huang, Cheng-Yu Yu, Zih-Wei Cyue, Jou-Chun Lin, Chun-Chih Chang, Shao-Sian Li*, Bing Joe Hwang, Chun-Wei Chen*, Di-Yan Wang*
https://doi.org/10.1016/j.carbon.2026.121250
Bias-free photoelectrochemical (PEC) seawater splitting has emerged as an attractive technology for solar-to-hydrogen (STH) conversion. This work demonstrates a promising alternative by replacing the sluggish kinetics of the oxygen evolution reaction (OER) with iodide oxidation reaction (IOR), which requires a much lower oxidation potential of 0.53 V vs. RHE. This approach facilitates bias-free solar-to-hydrogen (STH) conversion directly from natural seawater while simultaneously producing high-value triiodide (I3–) chemicals. An atomic layer of graphene functions as an efficient catalyst for PEC IOR when integrated with a Si heterojunction photoanode, exhibiting a promising PEC IOR with a low onset potential of 0.05 V vs. RHE. The unique two-dimensional energy dispersion and delocalized π-electrons of graphene facilitate rapid charge transfer, thereby enhancing overall catalytic efficiency. In-situ Raman spectroscopic analysis was performed to manifest that In-situ Raman spectroscopy reveals that adsorbed iodide/iodine species will induce local lattice strain in graphene, which perturbs the coherence of phonon scattering in the π-system. Moreover, when coupled with a Pt/graphene/Si heterojunction photocathode for HER, a bias-free PEC system for STH and IOR can be simultaneously achieved. This system demonstrates remarkable performance and stability, yielding a high photocurrent density of 14.22 mA/cm2 for simulated seawater and 13.13 mA/cm2 for natural seawater without any applied bias under 1 sun illumination. The integrated graphene/Si heterojunction photoelectrodes provide a promising platform for developing stable and high-performance bias-free PEC cells, facilitating simultaneous STH conversion and producing valuable chemicals from.
