Enhanced Stability and Efficiency for Photoelectrochemical Iodide Oxidation by Methyl Termination and Electrochemical Pt Deposition on n-Type Si Microwire Arrays

• Published in: ACS energy letters 2019-09, Vol.4 (9), p.2308-2314
• Main Authors: Ardo, Shane, Santori, Elizabeth A, Emmer, Hal S, Grimm, Ronald L, Bierman, Matthew J, Brunschwig, Bruce S, Atwater, Harry A, Lewis, Nathan S
• Format: Article
• Language: English
• ISSN: 2380-8195; 2380-8195
• DOI: 10.1021/acsenergylett.9b01529

Arrays of Si microwires doped n-type (n-Si) and surface-functionalized with methyl groups have been used, with or without deposition of Pt electrocatalysts, to photoelectrochemically oxidize I–(aq) to I3 –(aq) in 7.6 M HI­(aq). Under conditions of iodide oxidation, methyl-terminated n-Si microwire arrays exhibited stable short-circuit photocurrents over a time scale of days, albeit with low energy-conversion efficiencies. In contrast, electrochemical deposition of Pt onto methyl-terminated n-Si microwire arrays consistently yielded energy-conversion efficiencies of ∼2% for iodide oxidation, with an open-circuit photovoltage of ∼400 mV and a short-circuit photocurrent density of ∼10 mA cm–2 under 100 mW cm–2 of simulated air mass 1.5G solar illumination. Platinized electrodes were stable for >200 h of continuous operation, with no discernible loss of Si or Pt. Pt deposited using electron-beam evaporation also resulted in stable photoanodic operation of the methyl-terminated n-Si microwire arrays but yielded substantially lower photovoltages than when Pt was deposited electrochemically.