Decoupling H 2 (g) and O 2 (g) production in water splitting by a solar-driven V 3+/2+ (aq,H 2 SO 4 )|KOH(aq) cell

Alec Ho, Xinghao Zhou, Lihao Han, Ian Sullivan, Christoph Karp, Nathan S. Lewis, Chengxiang Xiang

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Abstract

A solar-driven V 3+/2+ (aq,H 2 SO 4 )|KOH(aq) cell, consisting of a carbon-cloth cathode in 2.0 M H 2 SO 4 (aq) with 0.36 M V 2 (SO 4 ) 3 (pH â'0.16), a Ni mesh anode in 2.5 M KOH(aq) (pH 14.21) for the oxygen-evolution reaction (OER), and a bipolar membrane that sustained the pH differentials between the catholyte and anolyte, enabled water splitting with spatial and temporal decoupling of the hydrogen evolution reaction (HER) from the OER and produced H 2 (g) locally under pressure upon demand. Over a range of potentials and charging depths, V 3+ was selectively reduced with >99.8% faradic efficiency. The V 2+ species produced in the catholyte was then passed subsequently on demand over a MoC x -based HER catalyst to produce H 2 (g) and regenerate V 3+ for subsequent reduction. Under a base hydrogen pressure of 1, 10, and 100 atm, the discharge efficiency of the V 3+ to hydrogen was 83%, 65.2%, and 59.8%, respectively. In conjunction with a solar tracker and a photovoltaic device, the V 3+/2+ (aq,H 2 SO 4 )|KOH(aq) cell was charged outdoors under sunlight and discharged at night with a daily averaged diurnal solar-to-hydrogen (STH) energy conversion efficiency of 3.7% and a STH conversion efficiency of 5.8% during daylight operation.

Original languageEnglish
Pages (from-to)968-976
Number of pages9
JournalACS Energy Letters
Volume4
Issue number4
DOIs
Publication statusPublished - Apr 12 2019

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ASJC Scopus subject areas

  • Chemistry (miscellaneous)
  • Renewable Energy, Sustainability and the Environment
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Materials Chemistry

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