Bulk and surface charge recombination of photoelectrode are two key processes that significantly hinder solar-to-fuel conversion of photoelectrochemical cell (PEC). In this study, the function of a “crystal-deficient” overlayer is unveiled, which outperforms a traditionally used amorphous or crystalline overlayer in PEC water splitting by exhibiting a high conductivity and large electron diffusion length to enable unlimited electron collection. The optimized ≈2.5 nm thickness of the “crystal-deficient” shell results in a depletion layer with a width of 3 nm, which overcomes the flat band limitation of the photovoltage and increases the light absorptivity in the wavelength range from 300 to 420 nm. In addition, a 50-fold increase in the conductivity yields a one-order-of-magnitude increase in the diffusion length of an electron (Ln)(≈20 μm), allowing for unlimited electron collection in the 1.9 μm TiO2 nanowire array with the “crystal-deficient” shell. The controllable “crystal-deficient” overlayer in rutile TiO2 nanowires photoanode achieves a photocurrent density greater than 2.0 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE), a 1.18% applied bias photon-to-current efficiency at 0.49 V versus RHE, a faradaic efficiency greater than 93.5% at 0.6 V versus Pt under air mass 1.5G simulated solar light illumination (100 mW cm−2).
Bibliographical noteFunding Information:
K.Z. and S.R. contributed equally to this work. This work was supported by the NRF of Korea Grant funded by the Ministry of Science, ICT, and Future Planning (NRF-2013R1A2A1A09014038, 2015M1A2A2074663, 2016M3D3A1A01913254 (C1 Gas Refinery Program)). This work was supported in part by the Yonsei University Future-leading Research Initiative of 2015 (2015-22-0067). S.R. thanks the Santiago Grisolía program from Generalitat Valenciana for its financial support under the grant 2014/034. The work at INAM-UJI was supported by the Generalitat Valenciana project PROMETEOII/2014/020.
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All Science Journal Classification (ASJC) codes
- Renewable Energy, Sustainability and the Environment
- Materials Science(all)