Light-assisted electrochemical water-splitting at very low bias voltage using metal-free polythiophene as photocathode at high pH in a full-cell setup

Kouki Oka, Orie Tsujimura, Takeo Suga, Hiroyuki Nishide, Bjorn Winther Jensen

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

We report the use of polyterthiophenes (PTTh) as a rare, combined light-harvester and catalyst for the hydrogen evolution reaction at high pH. Illuminated PTTh in combination with a MnOx anode in a two-electrode setup exhibited stable water-splitting at a bias-potential of only 0.3 V at pH 12. This confirms that PTTh used as photocathode can produce photovoltages of at least 900 mV for the hydrogen evolution reaction at high pH and is therefore a suitable match for traditional water-oxidation catalysts such as MnOx, CoOx, and RuOx. Films of PTTh were fabricated using a novel, metal-free method where iodine vapor is used as oxidant; thus, previously observed interference from metal residuals was omitted and thereby a gravimetric photo electrocatalytic conversion rate of 330 mmol(H2) h-1 g-1 was achieved in phosphate buffer (pH 7) at 0 V vs. RHE. A striking property of this new strand of polythiophene was an "inverse" correlation (compared to that predicted using the Nernstian relationship) between the onset potential for the light-assisted water reduction reaction and pH: the potential (vs. RHE) required for a given current was more positive at higher pH, which is not observed for other (photo-) electrocatalytic materials, and indicates that the charge neutralization of PTTh (rather than the pH) guides the onset potential.

Original languageEnglish
Pages (from-to)1335-1342
Number of pages8
JournalEnergy and Environmental Science
Volume11
Issue number5
DOIs
Publication statusPublished - 2018 May 1

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Photocathodes
Bias voltage
Metals
Water
Hydrogen
metal
Polymers
catalyst
hydrogen
Catalysts
Harvesters
neutralization
iodine
Iodine
Oxidants
oxidant
water
Buffers
Anodes
electrode

ASJC Scopus subject areas

  • Environmental Chemistry
  • Renewable Energy, Sustainability and the Environment
  • Nuclear Energy and Engineering
  • Pollution

Cite this

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abstract = "We report the use of polyterthiophenes (PTTh) as a rare, combined light-harvester and catalyst for the hydrogen evolution reaction at high pH. Illuminated PTTh in combination with a MnOx anode in a two-electrode setup exhibited stable water-splitting at a bias-potential of only 0.3 V at pH 12. This confirms that PTTh used as photocathode can produce photovoltages of at least 900 mV for the hydrogen evolution reaction at high pH and is therefore a suitable match for traditional water-oxidation catalysts such as MnOx, CoOx, and RuOx. Films of PTTh were fabricated using a novel, metal-free method where iodine vapor is used as oxidant; thus, previously observed interference from metal residuals was omitted and thereby a gravimetric photo electrocatalytic conversion rate of 330 mmol(H2) h-1 g-1 was achieved in phosphate buffer (pH 7) at 0 V vs. RHE. A striking property of this new strand of polythiophene was an {"}inverse{"} correlation (compared to that predicted using the Nernstian relationship) between the onset potential for the light-assisted water reduction reaction and pH: the potential (vs. RHE) required for a given current was more positive at higher pH, which is not observed for other (photo-) electrocatalytic materials, and indicates that the charge neutralization of PTTh (rather than the pH) guides the onset potential.",
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AU - Suga, Takeo

AU - Nishide, Hiroyuki

AU - Winther Jensen, Bjorn

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