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Alkali Cation Engineered Chemical Self‐Oxidation of Copper Oxide Nanowire‐Based Photocathodes

Von Wiley-VCH zur Verfügung gestellt

Do it yourself: Hydration enthalpy difference of Li+, Na+, and K+ in aqueous solution is used for chemical self-oxidation without an external applied bias. The thickness of the cation/H2O double layer is controlled. Li+ ions are strongly attracted to H2O. This forms a sufficient OH layer on the substrate. By accelerating the oxidation reaction, a CuO-free Cu2O nanowire photocathode is obtained.


Abstract

Hydrogen energy production through photoelectrochemical (PEC) water splitting has great potential in the field of renewable energy. This study focuses on the hydration enthalpy difference of cations (Li+, Na+, and K+) in an aqueous solution for the chemical self-oxidation process without an external applied bias. The thickness of the cation/H2O double layer is controlled. The starting materials are low-cost copper foil and the synthesis uses alkali cation-engineered chemical self-oxidation. Li+ ions are strongly attracted to water molecules. This forms a sufficient OH layer on the Cu foil surface. By accelerating the oxidation reaction, a large surface area of Cu(OH) x nanowires (NWs) with high purity and a uniform shape are obtained. This optimal p-type Cu2O NWs photocathode is CuO-free, has the highest conductivity, and is fabricated through phase transition using precise vacuum annealing. The other alkali cations produce the Cu2O/CuO mixed or CuO phases that degrade the PEC performances with severe corrosive reactions. The Cu/Li : Cu2O/AZO/TiO2/Pt photocathode has a 50 h stability with a photocurrent density of 8.4 mA cm−2 at 0 VRHE. The fabricated photoelectrode did not structurally collapse after stability measurements during this period. The captured hydrogen production was in agreement with the calculated faradaic efficiency.

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