Efficient Electrocatalytic Water Oxidation by a Copper Oxide Thin Film in Borate Buffer

A robust water oxidation catalyst based on copper oxide was prepared by facile electrodeposition of Cu²⁺ from borate buffer solution under near neutral conditions. The Cu–B_i thin film exhibits high activity and long-term stability in Cu²⁺-free pH 9 borate buffer. A steady current density of 1.2 mA/cm² was sustained for at least 10 h at 1.3 V versus NHE without iR compensation, which sets a new benchmark for copper-based OEC

Visible Light-Driven Water Oxidation Promoted by Host–Guest Interaction between Photosensitizer and Catalyst with A High Quantum Efficiency

A highly active supramolecular system for visible light-driven water oxidation was developed with cyclodextrin-modified ruthenium complex as the photosensitizer, phenyl-modified ruthenium complexes as the catalysts, and sodium persulfate as the sacrificial electron acceptor. The catalysts were found to form 1:1 host–guest adducts with the photosensitizer. Stopped-flow measurement revealed the host–guest interaction is essential to facilitate the electron transfer from catalyst to sensitizer. As a result, a remarkable quantum efficiency of 84% was determined under visible light irradiation in neutral aqueous phosphate buffer. This value is nearly 1 order of magnitude higher than that of noninteraction system, indicating that the noncovalent incorporation of sensitizer and catalyst is an appealing approach for efficient conversion of solar energy into fuels

Fabrication and Kinetic Study of a Ferrihydrite-Modified BiVO₄ Photoanode

In spite of great progress in the surface modification of semiconductor photoelectrodes, the role of the metal oxide cocatalyst on photoelectrochemical (PEC) performance is still not well understood. In this study, ferrihydrite (Fh) as a novel cocatalyst was decorated on a wormlike nanoporous BiVO₄ photoanode. A surface kinetics study of Fh/BiVO₄ by intensity-modulated photocurrent spectroscopy (IMPS) evidences the primary role of Fh on PEC performance enhancement, varying with the loading of Fh. It was found that dispersed Fh nanoparticles accelerate hole transfer for water oxidation, but the resulting photoanode suffers from poor stability. The thick layers of Fh address the stability of the electrode by suppressing surface charge recombination but result in reduced hole transfer rates. Modification of a BiVO₄ film with optimally thick layers of discrete nanoflakes effectively reduces charge recombination without compromising stability, leading to a high AM 1.5 G photocurrent of 4.78 mA/cm² at 1.23 V versus the reversible hydrogen electrode and an applied bias photon to current efficiency of 1.81% at 0.61 V. These values are comparable to the best results reported for undoped BiVO₄

Electrochemical and Photoelectrochemical Water Oxidation by Supported Cobalt–Oxo Cubanes

Cobalt–oxo cubane clusters were immobilized on a Nafion film-coated fluorine-doped tin oxide (FTO) electrode and an α-Fe₂O₃ photoanode as surface catalysts for water oxidation. The performance of electrochemical water splitting indicated that these earth-abundant metal complexes retain their homogeneous reactivity on the electrode. Furthermore, efficient visible light-driven water oxidation was realized by coupling a molecular electrocatalyst with an inorganic semiconductor as a noble metal-free photoanode, showing a stability significantly improved with respect to that of the homogeneous system

Defective and “<i>c</i>‑Disordered” Hortensia-like Layered MnO_<i>x</i> as an Efficient Electrocatalyst for Water Oxidation at Neutral pH

The development of a highly active manganese-based water oxidation catalyst in the design of an ideal artificial photosynthetic device operating under neutral pH conditions remains a great challenge, due to the instability of pivotal Mn³⁺ intermediates. We report here defective and “<i>c</i>-disordered” layered manganese oxides (MnO_<i>x</i>-300) formed on a fluorine-doped tin oxide electrode by constant anodic potential deposition and subsequent annealing, with a catalytic onset (0.25 mA/cm²) at an overpotential (η) of 280 mV and a benchmark catalytic current density of 1.0 mA/cm² at an overpotential (η) of 330 mV under neutral pH (1 M potassium phosphate). Steady current density above 8.2 mA/cm² was obtained during the electrolysis at 1.4 V versus the normal hydrogen electrode for 20 h. Insightful studies showed that the main contributing factors for the observed high activity of MnO_<i>x</i>-300 are (i) a defective and randomly stacked layered structure, (ii) an increased degree of Jahn–Teller distorted Mn³⁺ in the MnO₆ octahedral sheets, (iii) effective stabilization of Mn³⁺, (iv) a high surface area, and (v) improved electrical conductivity. These results demonstrate that manganese oxides as structural and functional models of an oxygen-evolving complex (OEC) in photosystem II are promising catalysts for water oxidation in addition to Ni/Co-based oxides/hydroxides