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The efficiency of hole extraction and transfer at electrode/electrolyte interface is one of the most important bottlenecks of BiVO4 photoanodes for photoelectrochemical (PEC) water splitting. Here, a huge improvement of surface charge transfer efficiency (ηsurface) of BiVO4 photoanode was achieved by surface modification of oxygen vacancy-abundant carbon quantum dots (OV-CQDs), in which the OV-CQDs serve as superfast hole transport channel for the fact that the abundant OV in OV-CQDs could induce the outward driving forces for hole trapping and migration at electrode/electrolyte interface. The OV-CQDs/BiVO4 shows the ηsurface value of 74.3% at 0.65 V vs. RHE (VRHE), which is 7.1 and 3.3 times higher than BiVO4 and CQDs/BiVO4, respectively. Besides, the OV-CQDs efficiently promote the bulk charge separation and UV-vis light harvesting of BiVO4. Therefore, the OV-CQDs/BiVO4 exhibits remarkable photocurrent densities of 2.76 mA cm-2 at 0.65 VRHE and 4.01 mA cm-2 at 1.23 VRHE, which are 12.5 and 3.4 times higher than BiVO4, 3.5 and 2.6 times higher than CQDs/BiVO4, respectively.

Severe bulk charge recombination, sluggish oxygen evolution reaction (OER) kinetics and poor visible light harvesting are still the technical bottlenecks of famous TiO2 photoanode for photoelectrochemical (PEC) water splitting. Here, a novel CQDs/E-TiO2 photoanode was designed based on the accurately electrochemical reduction of TiO2 (E-TiO2, Ti4+ + e− → Ti3+) and further modification of oxygen vacancy (OV)-rich carbon quantum dots (CQDs) for synergistically improving PEC performance. The electrochemical reduction creates moderate OV in TiO2, which increase the majority carrier density and provide photoinduced charge traps for sharply increasing the bulk charge separation efficiency (ηbulk). The CQDs modification dramatically improves the surface charge transfer efficiency (ηsurface) by serving as oxygen evolution catalysts (OECs), because the abundant OV in CQDs greatly promote the interfacial OER kinetics. Additionally, the visible light harvesting of TiO2 is significantly improved after CQDs modification. Near-complete bulk charge separation (ηbulk = 94.7%) is achieved for E-TiO2 at 1.23 V vs. RHE (VRHE), which is 4.0 times higher than that of TiO2. The CQDs/E-TiO2 shows the ηsurface of 56.0% at 0.40 VRHE, which is 7.2 times higher than E-TiO2. Therefore, the CQDs/E-TiO2 exhibits remarkable photocurrent densities of 1.50 mA cm−2 at 0.60 VRHE and 2.55 mA cm−2 at 1.23 VRHE, which are 27.0 and 10.0 times higher than TiO2, 3.5 and 1.5 times higher than E-TiO2, respectively.

In this study, an efficient WO3−x nanoplates photoanode was generated based on bidentate hydrogen bonds and in subsequent thermal reduction of ethylene glycol (EG). An appropriate number of controllable oxygen vacancies (Ov) was generated in-situ on the surface of the WO3 nanoplates without deep defects by bidentate hydrogen bonds. Density functional theory (DFT) calculations indicate that the distance between two alcoholic hydrogens (5.124 A) in EG matches that of the diagonal oxygens (5.483 A) in the WO3 (0 0 2) surface, which allows EG to combine through the most stable bidentate hydrogen bonds with O–H intervals of approximately 2.5 A. Diagonal oxygens are captured directly from the surface, leaving Ov owing to the special hydrogen-bond structure and moderate reducibility of EG under appropriate thermal conditions. The photocurrent density of the WO3−x nanoplates improves considerably to 2.07 from the 0.91 mA cm−2 of pristine WO3 with the introduction of Ov, which demonstrates the superior surface reaction kinetics from the reduced holes-to-water resistance and increase in surface injection efficiency. DFT calculations of the oxygen evolution reaction reveal that surface Ov could substantially decrease the reaction energy barrier for a lower overpotential of 0.494 V compared to that of WO3 (1.037 V), which is consistent with the reduction in the Tafel slope from 412 to 243 mV dec−1. Therefore, this study provides an innovative method to obtain an efficient WO3 photoanode based on the treatment of EG.

Hydrogen generation by solar-driven water splitting is considered as a promising strategy to address energy crisis and environmental emission issues. Bismuth vanadate (BiVO4) is a highly promising photoanode material for photoelectrochemical (PEC) water splitting, but its severe bulk and surface charge recombination, sluggish oxygen evolution reaction (OER) kinetics and narrow visible light harvesting are still bottlenecks. Here, an excellent CQDs/FeOOH/BiVO4 photoanode was designed by co-modification of carbon quantum dots (CQDs) and ultrathin β-FeOOH layers (

Efficient separation and transport of charge is a critical issue in solar-driven water oxidation. Herein, we developed a novel, facile, controllable method based on zero-valent iron (ZVI) reduction to in-situ and synchronous generate oxygen vacancies (Ov) and FeOx oxygen evolution co-catalysts (OECs) on BiVO4 for ultrafast electron transfer and excellent photoelectrochemical (PEC) water oxidation. In this method, a moderate and controllable ZVI reduction was the critical step to ensure whole penetration of Ov from BiVO4 to FeOx layer. This is because a special galvanic cell is formed between ZVI and BiVO4, making it easy to capture oxygen atom from BiVO4 and obtain a FeOx layer (5 nm) outside simultaneously in oxygen-free annealing. The Ov can extend light absorption by narrowing bandgap and significantly improve electron mobility (8.6 × 10−7 cm2 s−1) by reducing the trap-assisted recombination, which is 6.1-fold of BiVO4. Meanwhile, electron lifetime increases from 11.6 to 115.3 ms. Ultrathin FeOx layer provides more sites and dramatically reduces OER over-potential of 210 mV, resulting in fast hole-to-oxygen kinetics. A photocurrent of 3.13 mA·cm−2 at 1.23 VRHE is achieved for PEC water oxidation, which is 4.6-fold of pristine BiVO4. This work provides a new path to overcome charge transport limitations and achieve enhanced solar water oxidation.

The use of a photocatalytic fuel cell (PFC) in wastewater treatment is an intensively researched topic because the device integrates organic pollutant degradation and chemical energy recovery. Herein, we proposed a strategy to enhance PFC performance by increasing the concentrations of hydroxyl radical (HO ) and superoxide radical (O2− ) produced from H2O2 generated in situ using an activated graphite felt (GF) cathode. This cathode was prepared by H2SO4 treatment to introduce oxygen-containing functional groups on its surface that would serve as surface-active sites and facilitate the two-electron pathway of H2O2 production. Remarkably, the peak current density of the activated GF cathode (−1.25 mA/cm2) was more than thrice that of the original GF cathode (−0.40 mA/cm2), and its Faradaic efficiency significantly improved from 20.01% to 74.09%. The PFC equipped with the activated GF cathode harvested 2.69 times the maximum power density (JVmax) and 5.15 times the degradation rate of the traditional Pt black-PFC system. This was because the O2 − and HO concentrations, respectively, were 2.87 (23.98 × 10−5 M) and 2.48 times (13.00 × 10−4 M) as high as those in the Pt black-PFC system. These results were attributed to the high concentration of H2O2 generated in situ at the activated GF cathode, which was 25.13 times (0.402 mM) as high as that generated at the Pt black cathode. Thus, the proposed PFC system demonstrates the feasibility of improving organic pollutant degradation and energy recovery by enhancing H2O2 production.

N-containing organic wastewater is harmful to human health and ecosystem while its degradation remains a huge challenge for decarburization and denitrification simultaneously. In this paper, we proposed a new photoelectrochemical method of chlorine oxide radicals production to oxidize mixture wastewater of phenol and N-ammonia into N2 and CO2. The chlorine oxide radicals were generated via a rapid reaction of HClO with hydroxyl radicals or chlorine free radicals on a synergistic dual anode, in which hydroxyl radicals and chlorine free radicals generated on WO3 side, and HClO generated on Sb-SnO2 side, respectively. Phenol degradation rate on WO3-Sb/SnO2 was 2.54 and 4.79 times than that on WO3 and Sb/SnO2. Meanwhile, N-ammonia removal rate on WO3-Sb/SnO2 was 5.69 and 20 times greater than that on WO3 and Sb/SnO2, respectively. The effects of potential, Cl− concentration and initial pH were examined and the optimal conditions were potential 2.0 V vs Ag/AgCl, 0.05 M NaCl, pH = 5. The free radical quenching experiments and electron-spin resonance (ESR) confirmed that chlorine oxide radicals played an important role in the degradation of N-ammonia and phenol. Reasonable pathways of phenol in the WO3-Sb/SnO2 system were also proposed. This work provides an exhaustive, novel, environmental-friendly photoelectrochemical system for N-containing organic wastewater treatment.