Efficient Photoelectrochemical Water Research Articles

Defect Anchoring [S–Ni–P] Interfacial Channel Regulating Charge Migration for Efficient Photoelectrochemical Water Splitting

AbstractRegulating bulk charge carrier transfer and surface catalytic reaction kinetics is thought a big challenge to photoelectrochemical (PEC) water splitting. Herein, the dual sites of CoNiP are delicately introduced into ZnIn2S4 (RZIS‐CoNiP) nanosheet arrays via a defect anchoring method. The paving [S─Ni─P] interfacial bond like a “bridge” can greatly reduce the phase resistance, improve the charge separation and migration, and promote the surface oxygen evolution reaction (OER) reaction. As expected, the optimized RZIS‐CoNiP photoanode achieved a maximum photocurrent density of 4.77 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE) in neutral electrolyte solution without the presence of any sacrificial agents, which is ≈12 times higher than that of the pristine ZnIn2S4 under AM 1.5G illumination. And the amount of oxygen evolution for the RZIS‐CoNiP photoanode is as high as 21.9 µmol in 3 h. Transient spectroscopy measurements and density functional theory (DFT) calculations in situ discovered the mechanism of defect anchoring [S─Ni─P] bond on regulating charge transfer and surface reaction processes. This work provides a feasible anchoring interface route through defect engineering to regulate charge carrier transfer for PEC water splitting.

Regulating the binding strength of oxygen intermediates with a conductive π–d conjugated metal-organic polymer CoTAA on BiVO4 photoanode for efficient photoelectrochemical water oxidation

The slow charge transfer and sluggish water oxidation reaction kinetics represent the main obstacles in the advancement of efficient BiVO4 photoanodes for photoelectrochemical (PEC) water splitting. Herein, a conductive π-d conjugated metal–organic polymer composed of 1,4,8,11-tetraaza[14]annulene (TAA) and atomically dispersed Co sites (CoTAA) was developed as an efficient oxygen evolution catalyst (OEC) to overcome these limitations. In CoTAA, the highly delocalized π-d conjugation results in superior electrical conductivity, leading to improved charge transfer. Additionally, X-ray absorption fine structure (XAFS) spectra and theoretical simulations reveal that the atomically dispersed Co sites within CoTAA, configured as Co-N4, modulates the binding strength of water oxidation intermediates (*OH, *O, and *OOH), thereby decreasing the energy barrier and facilitating the water oxidation reaction kinetics. Consequently, when combining with ultrathin FeOOH withdrawing the holes, the optimized CoTAA/FeOOH/BiVO4 photoanode achieves a high photocurrent density of 4.97 mA cm−2 at 1.23 VRHE under one sun irradiation (100 mW cm−2). This photocurrent represents a 2.59-fold enhancement when compared to that of pure BiVO4. These findings demonstrate the tremendous potential of π-d conjugated metal–organic polymers as active OECs in enhancing the PEC performance of water splitting.

Heterostructured WO3–TiVO4 thin-film photocatalyst for efficient photoelectrochemical water splitting

Photoelectrochemical water splitting via solar irradiation has garnered significant interest due to its potential in large-scale renewable hydrogen production. Heterostructure materials have emerged as an effective strategy, demonstrating enhanced performance in photoelectrochemical water-splitting applications compared to individual photocatalysts. In this study, to augment the performance of sprayed TiVO4 thin films, a hydrothermally prepared WO3 underlayer was integrated beneath the spray pyrolised TiVO4 film. The consequent heterostructure demonstrated notable enhancements in optical, structural, microstructural attributes, and photocurrent properties. This improvement is attributed to the strategic deposition of WO3 underlayer, forming a heterostructure composite electrode. This led to a marked increase in photocurrent density for the WO3/TiVO4 photoanode, reaching a peak of 740 μA/cm2 at an applied potential of 1.23 V vs RHE, about nine-fold that of standalone TiVO4. Electrochemical impedance spectroscopy revealed a reduced semicircle for the heterostructure, indicating improved charge transfer compared to bare TiVO4. The heterostructure photoelectrode exhibited enhanced charge carrier conductivity at the interface and sustained stability over 3 h. The distinct attributes of heterostructure photoelectrode present significant opportunities for devising highly efficient sunlight-driven water-splitting systems.

A tungsten phosphide cocatalyst enhanced bismuth tungstate photoanode with the robust built-in electric field towards highly efficient photoelectrochemical water splitting

The use of low-cost and effective cocatalyst is a potential strategy to optimize the effectiveness of photoelectrochemical (PEC) water splitting. In this study, tungsten phosphide (WP) is introduced as a remarkably active cocatalyst to enhance the PEC efficiency of a Bi2WO6 photoanode. The onset potential of Bi2WO6/WP demonstrates a negative shift, while the photocurrent density demonstrates a significant 5.5-fold increase compared to that of unmodified Bi2WO6 at 1.23 VRHE (reversible hydrogen electrode). The loading of WP cocatalyst facilitates the rapid transfer of holes, increasing the range of visible light absorption, the water adsorption ability as well as promoting the separation of photogenerated electrons and holes via the built-in electric field between Bi2WO6 and WP. This study proposes a strategy to hinder the recombination of electron-hole pairs by using WP cocatalyst as a hole capture agent, improve the photoelectric conversion efficiency, and enhance the overall photoelectrochemical properties of Bi2WO6 photoanode.

An Interface-cascading Silicon Photoanode with Strengthened Built-in Electric Field and Enriched Surface Oxygen Vacancies for Efficient Photoelectrochemical Water Splitting.

To promote interfacial charge transfer process and accelerate surface water oxidation reaction kinetics for photoelectrochemical (PEC) water splitting over n-type Silicon (n-Si) based photoanodes, herein, starting with surface stabilized n-Si/CoOx , a NiOx /NiFeOOH composite overlayer was coated by atomic layer deposition and spray coating to fabricate the multilayer structured n-Si/CoOx /NiOx /NiFeOOH photoanode. Encouragingly, the obtained n-Si/CoOx /NiOx /NiFeOOH photoanode exhibits much increased PEC activity for water splitting, with onset potential cathodically shifted to ~0.96 V vs. RHE and photocurrent density increased to 22.6 mA cm-2 at 1.23 V vs. RHE for OER, as compared to n-Si/CoOx , even significantly surpassing the counterpart n-Si/CoOx /NiOx /FeOOH and n-Si/CoOx /NiOx /NiOOH photoanodes. Photophysical and electrochemical characterizations evidence that the deposited CoOx /NiOx /NiFeOOH composite overlayer would create large band bending and strong built-in electric field at the introduced cascading interfaces, thereby producing a large photovoltage of 650 mV to efficiently accelerate charge transfer from the n-Si substrate to the electrolyte for water oxidation. Furthermore, the surface oxygen vacancy enriched NiFeOOH overlayer could effectively catalyze the water oxidation reaction by thermodynamically reducing the energy barrier of rate determining step for OER.

WO3/FeOOH heterojunction for improved charge carrier separation and efficient photoelectrochemical water splitting

Photoanodes with sufficient visible light absorption, efficient photogenerated carrier separation and fast transport are still the main challenges for realizing high-efficiency photoelectrochemical (PEC) water splitting. Herein, we prepared the WO3/FeOOH heterojunction in situ grown on the FTO glass substrates by a facile seed-mediated two-step hydrothermal method. Under simulated sunlight irradiation, the prepared WO3/FeOOH heterojunction exhibits the enhanced photocurrent density of 2.63 mA cm−2 at 1.23 V vs. RHE, which is much higher than that of the bare WO3 film (1.62 mA cm−2 at 1.23 V vs. RHE). The excellent PEC performance of the sample can be attributed to the improved oxygen evolution kinetics and the extended visible light absorption range due to FeOOH, and the facilitation of carrier separation together with the suppressed recombination of photogenerated electron-hole pairs due to the formation of type-II WO3/FeOOH heterojunction. This work provides a promising approach for developing a highly efficient and cost-effective photoanode for application in solar-driven PEC water splitting.

Sonochemical surface modification of a novel Sm2O3@g-C3N4@Bi2O3 ternary hybrid photocatalyst exhibiting efficient solar light harvesting: Degradation of Azure b and photoelectrochemical water splitting

Engineered Z-scheme photocatalysts have a strong redox activity while also reducing the annihilation of light-induced charge bearers. In this investigation, a solid state twin Z-scheme Sm2O3@g-C3N4@Bi2O3 nanocomposite has been successfully prepared employing bismuth (III) nitrate, samarium chloride and urea as precursor chemicals in a single co-calcination procedure followed by sonochemical surface modification. The formation of flower like multiphasic material is confirmed from SEM and HRTEM images. BET findings suggested the enhancement in specific surface area of Sm2O3@g-C3N4@Bi2O3 and reduced band gap from UV–visible data. Photoluminescence results confirmed the reduction in rate of charge carrier recombination of Sm2O3@g-C3N4@Bi2O3. Presence of samarium is confirmed from XPS analysis. Under direct solar radiation, the surface modified Sm2O3@g-C3N4@Bi2O3 hybrid demonstrated amplified photo-assisted catalytic activity for the degradation of Azure B (AzB) than pristine g-C3N4 and their binary composite Sm2O3@g-C3N4. It is possible to attribute the better solar light absorption, higher separation efficacy of photo-promoted electron-holes to the amplified photo-assisted degradation performance of the Sm2O3@g-C3N4@Bi2O3 composite. The photodegradaton of AzB follows pseudo-first order kinetics and the observed rate constants are 0.0014, 0.0026, and 0.0316 min−1 for g-C3N4, Sm2O3@g-C3N4, and Sm2O3@g-C3N4@Bi2O3 ternary composite. The nanocomposite also demonstrates good stability and recyclability. A unique solid-state twin Z-scheme photocatalytic pathway was also hypothesized in light of the findings. The fabricated ternary hybrid shown efficient photoelectrochemical water splitting reaction for H2 and O2 generation.

Efficient synthesis of 3D ZnO nanostructures on ITO surfaces for enhanced photoelectrochemical water splitting

New photoactive materials with uniform and well-defined morphologies were developed for efficient and sustainable photoelectrochemical (PEC) water splitting and hydrogen production. The investigation is focused on hydrothermal deposition of zinc oxide (ZnO) onto indium tin oxide (ITO) conductive surfaces and optimization of hydrothermal temperature for growing uniform sized 3D ZnO morphologies. Fine-tuning of hydrothermal temperature enhanced the scalability, efficiency, and performance of ZnO-decorated ITO electrodes used in PEC water splitting. Under UV light irradiation and using eco-friendly low-cost hydrothermal process in the presence of stable ZnO offered uniform 3D ZnO, which exhibited a high photocurrent of 0.6 mA/cm2 having stability up to 5 h under light-on and light-off conditions. The impact of hydrothermal temperature on the morphological properties of the deposited ZnO and its subsequent performance in PEC water splitting was investigated. The work contributes to advancement of scalable and efficient fabrication technique for developing energy converting photoactive materials.

Efficient Acidic Photoelectrochemical Water Splitting Enabled by Ru Single Atoms Anchored on Hematite Photoanodes.

Photoelectrochemical (PEC) water splitting in acidic media holds promise as an efficient approach to renewable hydrogen production. However, the development of highly active and stable photoanodes under acidic conditions remains a significant challenge. Herein, we demonstrate the remarkable water oxidation performance of Ru single atom decorated hematite (Fe2O3) photoanodes, resulting in a high photocurrent of 1.42 mA cm-2 at 1.23 VRHE under acidic conditions. Comprehensive experimental and theoretical investigations shed light on the mechanisms underlying the superior activity of the Ru-decorated photoanode. The presence of single Ru atoms enhances the separation and transfer of photogenerated carriers, facilitating efficient water oxidation kinetics on the Fe2O3 surface. This is achieved by creating additional energy levels within the Fe2O3 bandgap and optimizing the free adsorption energy of intermediates. These modifications effectively lower the energy barrier of the rate-determining step for water splitting, thereby promoting efficient PEC hydrogen production.

Enhanced solar-driven photoelectrochemical water splitting using nanoflower Au/CuO/GaN hybrid photoanodes.

Harnessing solar energy for large-scale hydrogen fuel (H2) production shows promise in addressing the energy crisis and ecological degradation. This study focuses on the development of GaN-based photoelectrodes for efficient photoelectrochemical (PEC) water splitting, enabling environmentally friendly H2 production. Herein, a novel nanoflower Au/CuO/GaN hybrid structure was successfully synthesized using a combination of methods including successive ionic layer adsorption and reaction (SILAR), RF/DC sputtering, and metal-organic chemical vapour deposition (MOCVD) techniques. Structural, morphological, and optical characteristics and elemental composition of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, and energy-dispersive X-ray (EDX) spectroscopy, respectively. PEC and electrochemical impedance measurements were performed for all samples. The nanoflower Au/CuO/GaN hybrid structure exhibited the highest photocurrent density of ∼4 mA cm-2 at 1.5 V vs. RHE in a Na2SO4 electrolyte with recorded moles of H2 of about 3246 μmol h-1 cm-2. By combining these three materials in a unique structure, we achieved improved performance in the conversion of solar energy into chemical energy. The nanoflower structure provides a large surface area and promotes light absorption while the Au, CuO, and GaN components contribute to efficient charge separation and transfer. This study presents a promising strategy for advancing sustainable H2 production via efficient solar-driven water splitting.

Plasma-induced N doping and carbon vacancies in a self-supporting 3C-SiC photoanode for efficient photoelectrochemical water oxidation

We report that a plasma-induced self-supporting 3C-SiC photoanode with N doping and carbon vacancies demonstrates high photocurrent density and stability for photoelectrochemical water oxidation in alkaline solution under simulated solar irradiation.

Engineering the transition metal hydroxide–photoanode interface with a highly crystalline mediator for efficient photoelectrochemical water splitting

A one-stone-two-birds strategy was developed to engineer the SC/TMH/electrolyte interface by introducing high crystallinity Fe(OH)X-H, and the optimized BV/Fe(OH)X-H/FeNi(OH)X exhibited a noteworthy photocurrent density of 5.34 mA cm−2.

Interfacial phosphate-like “bridge” mediates bulk charge and surface oxygenated-intermediate migration for efficient photoelectrochemical water splitting

The interfacial [PO] bonds pave a barrier-free “bridge” regulating the bulk charge and surface oxygenated-intermediate migration for boosting the oxygen evolution reaction.

Alkali-assisted synthesis of polymeric carbon nitride photoanodes with defect and crystallinity-mediated charge transfer for efficient photoelectrochemical water splitting

A PCN-based photoanode with an N-defect structure and improved crystallinity (KPCN) was developed using an alkali-assisted synthesis method, resulting in significantly enhanced PEC performance.

Composition modulation of a hematite photoanode for highly efficient photoelectrochemical water oxidation

In this work, oxygen vacancy (VO) and hydrogen (H) impurity defects were introduced to control the chemical composition of α-Fe2O3. Our work verifies the relationship between the semiconductor electrode performance and its composition and provides effective guidance for further optimization.

Molecular insights into the water dissociation and proton dynamics at the β-TaON (100)/water interface.

Understanding the dynamic nature of the semiconductor-water interface is crucial for developing efficient photoelectrochemical water splitting catalysts, as it governs reactivity through charge and mass transport. In this study, we employ ab initio molecular dynamics simulations to investigate the structural and dynamical properties of water at the β-TaON (100) surface. We observed that a well-defined interface is established through the spontaneous dissociation of water and the reorganization of surface chemical bonds. This leads to the formation of a partially hydroxylated surface, accompanied by a strong network of hydrogen bonds at the TaON-water interface. Consequently, various proton transport routes, including the proton transfer through "low-barrier hydrogen bond" path, become active across the interface, dramatically increasing the overall rate of the proton hopping at the interface. Based on our findings, we propose that the observed high photocatalytic activity of TaON-based semiconductors could be attributed to the spontaneous water dissociation and the resulting high proton transfer rate at the interface.

Modulation of charge-transfer behavior via adaptive interface treatment for efficient photoelectrochemical water splitting

We report a “one stone, three birds” strategy for efficiently suppressing the electron–hole recombination occurring at the SC/TMH interface. After acid treatment, optimized BV-HA/FeNi(OH)X photoanodes showed enhanced photocurrent density and excellent photostability.

(Invited) Highly Nanoporous Hematite with Optimal Doping for an Efficient Photoelectrochemical Water Splitting

In this study, we propose a highly nanoporous hematite structure having under 5 nm hole diffusion pathways via an optimized doping method based on Density Functional Theory (DFT) calculations. The superiority of highly nanoporous structure with the synergistic effects of a facilitated Kirkendall effect and optimal doping condition were clearly proved by the experimental analyses. The optimized prous photoanode prepared with an optimal doping conditoin (Ge:Ti:Sn doped hematite) and the subsequent dopositon of an oxygen evolution reaction co-catalyst NiFe(OH)x showed a maximum photocurrent density of 5.1 mA cm-2 at 1.23 VRHE, which is 3.3-fold higher than that of reference Ti:Sn hematite due to enhanced surface reaction kinetics. This study provides a significant breakthrough in dramatically improving the low PEC performance of hematite-based photoanodes with an short-hole diffusion pathway issue through optimal co-doping and nanostructuring.

Ferroelectric spontaneous polarization assisted TiO2@BaTiO3@Ag photoanode for efficient photoelectrochemical water splitting via BaTiO3 phase regulation

In this work, TiO2@BaTiO3@Ag composite photoanodes were synthesized. By fabricating BaTiO3 with different phase structures, the influence of crystalline phase of BaTiO3 on PEC water splitting was investigated. Furthermore, hot electrons generated in the plasmonic effect of Ag nanoparticles can be efficiently injected into TiO2 film with the assistance of spontaneous polarization electric field (SPEF). Benefitting from this SPEF coupled plasmonic effect, the optimized TiO2@BaTiO3@Ag photoanode (T-TB@Ag) achieved a maximum photocurrent density of 7.30 mA cm−2 (1.23 V vs. RHE) under AM 1.5 G simulated sunlight, which is 6 times that of the non-ferroelectric cubic phase TiO2@BaTiO3@Ag photoanode (C-TB@Ag). This ferroelectric spontaneous polarization coupling plasmonic effect can effectively reduce carrier recombination and promote the separation of photocarriers, which ultimately increases PEC water splitting activity.

Rationally designed core-shell of 2D-g-C3N4/Cu2O nanowires heterojunction photocathode for efficient photoelectrochemical water splitting

Copper oxide (Cu2O) is a promising candidate as a high-performance photocathode due to its remarkable cost-to-efficiency ratio for photoelectrochemical (PEC) water splitting. However, fully exploiting the potential of planar Cu2O photocathodes for an efficient PEC performance remains a fundamental challenge owing to the poor light absorption and limited carrier diffusion length. To address these challenges, a graphitic carbon nitride (g-C3N4)/2D-Cu2O nanowires (NWs) with core-shell heterojunction photocathode has developed. The PEC water-splitting analysis reveals that the g-C3N4/Cu2O core-shell NWs photocathode boosted the photocurrent density from 0.83 mA/cm2 to 2.33 mA/cm2 at 0 VRHE (3-fold enhancement) compared with bare Cu2O. The formation of a g-C3N4 shell over the Cu2O core resulted in improved light harvesting as well as facile charge transport from the electrode to the electrolyte. Computational studies also revealed an impressive Gibbs free energy of 0.20 eV for the g-C3N4/Cu2O interface, highlighting its potential as an efficient PEC water-splitting device. These findings demonstrate that incorporating nanostructuring and overlayer strategies can remarkably enhance the PEC performance of Cu2O photocathodes, paving the way for more efficient and cost-effective water-splitting technologies.