Huang, Yung-HungYung-HungHuangWu, Po-HsienPo-HsienWuLu, Yang-ShengYang-ShengLuLin, Yin-ChengYin-ChengLinHuang, Chih-YingChih-YingHuangYu, Cheng-YuCheng-YuYuCyue, Zih-WeiZih-WeiCyueLin, Jou-ChunJou-ChunLinChang, Chun-ChihChun-ChihChangLi, Shao-SianShao-SianLiHwang, Bing JoeBing JoeHwangCHUN-WEI CHENWang, Di-YanDi-YanWang2026-03-122026-03-122026-02-1000086223https://www.scopus.com/record/display.uri?eid=2-s2.0-105027940718&origin=resultslisthttps://scholars.lib.ntu.edu.tw/handle/123456789/736237Bias-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 seawater.falseAtomic layer graphene catalystsBias-free solar to hydrogen conversionEVA graphene transfer methodIodide oxidation reactionPhotoelectrochemical celljournal article10.1016/j.carbon.2026.1212502-s2.0-105027940718