Tenorite CuO thin films have been synthesized via spray pyrolysis of aqueous copper(II) chloride solution followed by heat-treatment, exhibited a photocurrent density of 24 mA cm −2 at 0.25 V vs. RHE under AM 1.5G solar irradiation in alkaline electrolyte. This large photocurrent density has been attributed to a drift assisted transport of photo-generated electrons across the semiconductor/electrolyte interface in the annealed films. The tendency of photo-corrosion from the surface of CuO has been reduced substantially without any extra protective layer, simply by adding K 3 Fe(CN) 6 in the electrolyte, which acts as a sacrificial excess-electron scavenging agent. The fabricated electrode exhibited a positive onset potential at 0.25 V vs. RHE even after the electrolyte modification and a stable photocurrent density of more than 40% has been retained after 20 minutes of continuous illumination. The processed photocathode showed a solar to chemical conversion efficiency of 7.85% and 21.5% with and without using an electron scavenging agent, respectively. It holds the promise of using this photocathode in PEC energy conversion, photocatalysis and solar water splitting.In the exploration of terrestrially employable carbon-free energy sources, materials play a central role in the generation and storage of electrical as well as chemical energies. 1,2 Semiconducting materials are especially important to harvest the solar energy due to their bandgap energies matching to that of the visible photons. Photovoltaic (PV) and photoelectrochemical (PEC) methods are the two solar energy conversion modes those utilize semiconductor materials. In order to apply semiconductors in PEC applications, three important aspects must be satisfied: first, capability of providing large photocurrent density; second, a long term stability; and third, the scalability. 3 Several semiconductors, such as have been explored in the PEC applications with majority as catalysts for water splitting. The hunt for novel structure and materials design thus continues to set off the above requirements. Oxides of copper (CuO and Cu 2 O) have recently drawn special attention due to their relative abundance on the earth crust. Majority of the recently reported investigations are focused on Cu 2 O. [25][26][27][28][29][30][31][32] Due to the chemical instability and poor electron transfer, its nano-composites with other oxides or metal catalysts have been attempted. [33][34][35] On the other hand, CuO is chemically more stable than Cu 2 O but there are only few studies on the PEC response of CuO have been reported so far. 36 Among various oxides of copper (viz. Cu 2 O, CuO and Cu 4 O 3 ), tenorite CuO is a chemically stable p-type semiconductors having an indirect bandgap in the range of 1.3-1.7 eV. 37-42 This property makes CuO a promising candidate for solar to chemical energy conversion with maximum possible theoretical photocurrent density in the range of 22-35 mAcm −2 under standard AM 1.5G solar irradiance corresponding to its high and low bandgap values, ...

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Mercurochrome-sensitized nanostructured CuO grown directly on Cu has been used as efficient photocathode in photoelectrochemical cell. The photocurrent density of the sensitized electrode is found to enhance from −1 mA/cm2 (unsensitized) to −2.2 mA/cm2 (dye sensitized for 24 h) at 0 V vs RHE under AM1.5G artificial solar illumination in aqueous 0.5 M Na2SO4 solution. The photoluminescence spectra demonstrated a strong absorption at 465 nm by the mercurochrome. Subsequent transfer of the photoexcited electrons to CuO conduction band enhances the photocurrent density. An incident photon-to-current conversion efficiency (IPCE) of 8% has been observed in the visible region. This is so far the highest reported value in p-type CuO based organic dye-sensitized photocathode. The dye sensitized CuO has thus the potential of photoreduction with higher Faradaic efficiency for various redox species due to additional carrier injection.

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