Photoelectrochemical Water Oxidation Performance Research Articles

Coating effect of metal organic complex (Co-DTPMP) layer on enhancing PEC water oxidation performance of BiVO4 photoanode

Photoelectrochemical (PEC) water splitting is a promising method for transforming solar energy into clean and sustainable energy. However, PEC is severely limited, and they cannot achieve the predicted photocurrent density owing to the severe photochemical deterioration of the electrode and the recombination of photogenerated carriers. In this study, BiVO4/Co-diethylenetriamine Penta (methylene phosphonic acid) (BVO/Co-DTPMP) co-catalyst was successfully prepared as a nanoporous photoanode. Diethylenetriamine Penta (methylene phosphonic acid) was crosslinked with Co ions and coated on the BiVO4 surface by successive ionic layer adsorption and reaction (SILAR) to reduce fast recombination, which correlated with the BiVO4 photoanode. Various characterization and PEC measurements were conducted, revealing that the co-catalyst thin layer enhanced the charge separation and electrons transfer which significantly affected on the PEC performance of BiVO4, and the current density by BVO/Co-DTPMP was 4 mA cm−2 at 1.23 V vs. RHE. Furthermore, the co-catalyst exhibited improved charge transport and long-term stability.

Double oxygen evolution co-catalysts modified BiVO4 to boost photoelectrochemical water oxidation performance

Improving the kinetics of oxygen evolution is crucial for enhancing the performance of photoelectrochemical (PEC) water splitting. Herein, this study utilizes a chemical self-growth method to grow NiFe tannic acid complex (NFTA) and Co(OH)2 on the surface of BiVO4 photoanode (BiVO4/NFTA/Co). As a result, the synergistic effects of NFTA and Co(OH)2 layers promote the efficiency and stability of BiVO4 photoanode towards PEC water oxidation. The photocurrent density of the obtained BiVO4/NFTA/Co photoanode reaches 4.97 mA cm−2, which is significantly greater than those of BiVO4/NFTA (4.36 mA cm−2), BiVO4/Co (2.51 mA cm−2), BiVO4 (1.34 mA cm−2), respectively. Detailed analysis confirms that NFTA could provide an efficient way to hasten the transfer of photo-generated holes on the photoanode surface and diminish the surface charge transfer resistance. In other hand, Co(OH)2 could be served as a cocatalyst to accelerate charge transfer for efficient oxygen evolution reaction as well as a protective layer to maintain the long-term stability of NFTA on the surface of BiVO4 during water oxidation. Such double oxygen evolution co-catalysts decoration strategy paves an effective pathway to enhance the PEC water oxidation performance of BiVO4 photoanode.

Ternary Photoanodes with AgAu Nanoclusters and CoNi-LDH for Enhanced Photoelectrochemical Water Oxidation.

Atomically precise metal nanoclusters (NCs) present new opportunities for creating innovative solar-powered photoanodes due to their extraordinary physicochemical properties. Nevertheless, ultrasmall metal NCs tend to aggregate and lack active sites under light irradiation, which severely limits their widespread application. We have developed a strategy to design efficient ternary photoanodes by successively modifying AgAu NCs and CoNi-LDH on BiVO4 substrates using versatile impregnation and electrodeposition. The electronic properties of AgAu NCs facilitate the rapid transfer of photogenerated carriers on BiVO4 and CoNi-LDH. Additionally, ultrathin CoNi-LDH acts as a hole-collecting layer, which quickly extracts holes to the electrode/electrolyte interface. The synergistic effect and the matched energy levels between the ternary heterostructures promote the OER process, which significantly improved the photoelectrochemical (PEC) water oxidation performance. This study presents a new idea for further exploration of metal nanocluster-based PEC systems.

Boosting photoelectrocatalytic oxygen evolution activity of BiVO4 photoanodes via caffeic acid bridged to NiFeOOH

Bismuth vanadate (BiVO4) is a promising n-type photoanode material for photoelectrochemical (PEC) water splitting. However, its activity is impeded by poor charge carrier transport and sluggish oxygen evolution kinetics. In this study, we reports a Fe doping and caffeic acid (CA)/NiFeOOH (NiFe) modification with BiVO4 photoanode (NiFe/CA/Fe-BiVO4) to enhance the PEC water oxidation performance and stability. The modified BiVO4 demonstrates significant advantages in promoting the PEC performance and stability. Specifically, Fe doping via in-situ electro-deposition results in smaller crystal sizes, larger specific surface areas, and more exposed active sites. Furthermore, co-catalyst NiFe connects with Fe-BiVO4 through CA bridge facilitates a more uniform self-assembly distribution of NiFe on BiVO4 surface. The NiFe/CA/Fe-BiVO4 exhibits an excellent photocurrent density of 6.2 mA/cm2 at 1.23 VRHEand demonstrates good stability at 0.8 VRHE. In addition, the composite photoanode shows a high applied bias photon-to-current efficiency (ABPE) value of 2.15% at 0.65 VRHE. EPR and in-situ FTIR confirm the generation of superoxide active species (O2- and ·O2-) during the PEC water oxidation reaction.

The Role of Cobalt‐Based Cocatalysts on BiVO4 for Photoelectrochemical Water Oxidation

AbstractCocatalysts play a key role in enhancing activity of photoelectrodes while the study of their interaction remains a challenge. Here, we decoupled the relationship between oxygen evolution reaction (OER) performance and photoelectrochemical (PEC) water oxidation performance by modifying an identical BiVO4 with different cobalt‐based OER catalysts including Co, CoO, Co3O4, and Co4N. The electrochemical OER activities of these cobalt specimens were quite similar. Their anodic photocurrent density followed an order of: Co4N>Co>Co3O4>CoO after loading on the BiVO4 electrode. The kinetics process and energy band diagram were analyzed, revealing that the interface between different cobalt specimens and BiVO4 electrode influenced the charge recombination and transfer. Accordingly, we propose a corresponding structural model, which shows that the cocatalysts consist of inner part for interface modulation and the outer layer for catalysis. The present work reveals the vital role of contact interface between cocatalysts and semiconductors, and more attention should be paid when selecting the cocatalysts.

Profound influence of surface trap states on the utilization of charge carriers in CdS photoanodes

In CdS photoanodes, the decoration of surface sulfur vacancies by CTAB passivates the electron trapping process, resulting in improved photoelectrochemical water oxidation performance.

Fe-Ni porphyrin/mesoporous titania thin film electrodes: a bioinspired nanoarchitecture for photoelectrocatalysis.

Porphyrin and porphyrinoid derivatives have been extensively studied in the assembly of catalysts and sensors, seeking biomimetic and bioinspired activity. In particular, Fe and Ni porphyrins can be used for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by immobilization of these molecular catalysts on semiconductor materials. In this study, we designed a hybrid material containing a crystalline mesoporous TiO2 thin film in which the catalytic centres are Ni-porphyrin (NiP), Fe-porphyrin (FeP), and a NiP/FeP bimetallic system to assess whether the coexistence of both metalloporphyrins improves the OER activity. The obtained photoelectrodes were physicochemically and morphologically characterized through high-resolution FE-SEM images, UV-vis and Raman spectroscopies, cyclic voltammetry, and impedance measurements. The results show a differential behavior of the mono- and bimetallic porphyrin systems, where the Fe(iii) centre in FeP may increase the acidity and lower the reduction potential of the Ni2+/3+ couple when co-deposited with NiP leading to an improved photoelectrochemical water-oxidation performance. We have validated the cooperative effect of both metal complexes within this novel system, where the μ-peroxo-bridged interaction between Fe and Ni is integrated into a supramolecular heterometallic structure of porphyrins.

Enhancing photoelectrochemical surface reactivity through interface grafting of g-C3N4 quantum dots with BiVO4

Due to the high photosensitivity, quantum dots (QDs) offer promise in establishing heterojunctions to improve the photoelectrochemical (PEC) water oxidation process and enhance the solar-to-hydrogen conversion efficiency. However, apart from their catalytic capacity, additional protection strategies should be considered to eliminate the destruction of QDs from electrolytes and photo-corrosion. Here, we present a facile strategy to fabricate heterojunction by employing graphitic carbon nitride QDs (g-C3N4 QDs) coupled with BiVO4, referred to CNQDs/BiVO4. With the help of CNQDs, a gradient energy band alignment has been established in CNQDs/BiVO4, leading to facilitated hole migration driven by an upward force. The optimal CNQDs/BiVO4 sample shows significantly enhanced PEC performance for water oxidation, with a photocurrent of 2.2 mA/cm2 at 1.23 V vs. RHE (reversible hydrogen electrode), which is about 2.26 times better than that of BiVO4 (0.97 mA/cm2). The enhanced PEC performance could be attributed to the increased surface-active area and facilitated surface oxidation kinetics.

Synergy Effect of the Enhanced Local Electric Field and Built-In Electric Field of CoS/Mo-Doped BiVO4 for Photoelectrochemical Water Oxidation.

Bismuth vanadate is a promising material for photoelectrochemical water oxidation. However, it suffers from a low quantum efficiency, poor stability, and slow water oxidation kinetics. Here, we developed a novel photoanode of CoS/Mo-BiVO4 with excellent photoelectrochemical water oxidation performance. It achieved a photocurrent density of 4.5 mA cm-2 at 1.23 V versus the reversible hydrogen electrode, ∼4 times that of BiVO4. The CoS/Mo-BiVO4 photoanode also exhibited good stability, and the photocurrent density generated by the CoS/Mo-BiVO4 photoanode did not significantly decrease after light irradiation for 2 h. Upon replacement of part of the V with Mo doping in BiVO4, the local electric field around the Mo-O bond was enhanced, thus promoting carrier separation in BiVO4. The CoS was deposited on the surface of Mo-BiVO4, forming a built-in electric field at the interface. Under the action of the bias electric field and the built-in electric field, the carriers of CoS/Mo-BiVO4 were efficiently separated in the direction of the inverse type II heterojunction. In addition, CoS improved the light absorption and charge injection efficiency of the CoS/Mo-BiVO4 photoanode.

Synergistic effect between the iron (III) oxyhydroxide and Gd-Fe2O3 photoanode interface resulted in an ultra-low onset potential for photoelectrochemical water oxidation

The onset potential is an important descriptor of the photoelectrochemical water oxidation performance of photoanodes. Herein, we prepared Gd-doped hematite (Gd-Fe2O3)/iron (III) oxyhydroxide (FeOOH) core-shell photoanodes by in-situ isovalent doping and secondary hydrothermal treatment. This Gd-Fe2O3/FeOOH photoanode shows a record alkaline water oxidation onset potential (0.59 V vs. reversible hydrogen electrode) in hematite-based photoanodes and a 2.4-fold increase in photocurrent density over pristine hematite. Detailed studies demonstrate that the origin of the ultra-low onset potential is mainly attributed to the synergistic effect of isovalent Gd-doping and FeOOH cocatalyst. Specifically, Gd doping enhances donor density and reduces charge transport resistance, and FeOOH cocatalyst significantly improves water oxidation kinetics. In addition, the strong interfacial coupling of FeOOH and Gd-Fe2O3 promotes electron flow, which also improves the charge separation remarkably. This work gives hope for the achievement of stable and bias-free hematite-based photoanodes.

Enhanced photoelectrochemical water oxidation of a BiVO4/tetra(amino)phthalocyanine composite photoanode

We present a method for synthesizing a BiVO4composite photoanode using electrodeposition on FTO glass and show how the incorporation of tetra(amino)phthalocyanine (TAPC) improves its photoelectrochemical water oxidation properties. The conducted photocatalytic tests show that the incorporation of TAPC improved photocurrent generation, electron-hole generation, and separation as well as the stability of the BiVO4/TAPC composite material. The current densities of the pristine BiVO4and BiVO4/TAPC for photoelectrochemical water oxidation under operational conditions at 1.6 V vs. Ag/AgCl were found to be 1.7 and 3.1 mA cm[Formula: see text], respectively, which were estimated to be almost twice that of pristine BiVO4. The improved photoelectrochemical water oxidation performance of the BiVO4/TAPC composite may also be attributed to the enhanced surface area and surface redox reaction. These results demonstrate the potential of TAPC as a promising candidate for improving the performance of BiVO4photoanodes in various applications.

Architecture modification and In3+-doping of WO3 photoanodes to boost the photoelectrochemical water oxidation performance

Architecture modification and In3+-doping of WO3 photoanodes to boost the photoelectrochemical water oxidation performance

Porous 2D Catalyst Covers Improve Photoelectrochemical Water-Oxidation Performance.

Confined catalysis under the cover of 2D materials has emerged as a promising approach for achieving highly effective catalysts in various essential reactions. In this work, a porous cover structure is designed to boost the interfacial charge and mass transfer kinetics of 2D-covered catalysts. The improvement in catalytic performance is confirmed by the photoelectrochemical oxidation evolution reaction (OER) on a photoanode based on an n-Si substrate modified with a NiOx thin-film model electrocatalyst covered with a porous graphene (pGr) monolayer. Experimental results demonstrate that the pGr cover enhances the OER kinetics by balancing the charge and mass transfer at the photoanode and electrolyte interface compared to the intrinsic graphene cover and cover-free control samples. Theoretical investigations further corroborate that the pore edges of the pGr cover boost the intrinsic catalytic activity of active sites on NiOx by reducing the reaction overpotential. Furthermore, the optimized pores, which can be easily controlled by plasma bombardment, allow oxygen molecules produced in the OER to pass through without peeling off the pGr cover, thus ensuring the structural stability of the catalyst. This study highlights the significant role of the porous cover structure in 2D-covered catalysts and provides new insight into the design of high-performance catalysts.

Surface Self-Transforming FeTi-LDH Overlayer in Fe2 O3 /Fe2 TiO5 Photoanode for Improved Water Oxidation.

Integrating hematite nanostructures with efficient layer double hydroxides (LDHs) is highly desirable to improve the photoelectrochemical (PEC) water oxidation performance. Here, an innovative and facile strategy is developed to fabricate the FeTi-LDH overlayer decorated Fe2 O3 /Fe2 TiO5 photoanode via a surface self-transformation induced by the co-treatment of hydrazine and NaOH at room temperature. Electrochemical measurements find that this favorable structure can not only facilitate the charge transfer/separation at the electrode/electrolyte interface but also accelerate the surface water oxidation kinetics. Consequently, the as-obtained Fe2 O3 /Fe2 TiO5 /LDH photoanode exhibits a remarkably increased photocurrent density of 3.54mAcm-2 at 1.23V versus reversible hydrogen electrode (RHE) accompanied by an obvious cathodic shift (≈140mV) in the onset potential. This work opens up a new and effective pathway for the design of high-performance hematite photoanodes toward efficient PEC water oxidation.

Photoelectrodeposition of Ag3PO4 nanoparticles on BiVO4 photoanode for enhancing its photoelectrochemical water oxidation performance

Photoelectrodeposition of Ag3PO4 nanoparticles on BiVO4 photoanode for enhancing its photoelectrochemical water oxidation performance

MoOx layer with abundant oxygen vacancies modified on Sn-doped α-Fe2O3 film for enhanced photoelectrochemical water oxidation performance

MoOx layer with abundant oxygen vacancies modified on Sn-doped α-Fe2O3 film for enhanced photoelectrochemical water oxidation performance

Ultrathin TiO2 Blocking Layers via Atomic Layer Deposition toward High-Performance Dye-Sensitized Photo-Electrosynthesis Cells

The collection of solar energy in chemical bonds via dye-sensitized photoelectrosynthesis cells (DSPECs) is a reliable solution. Herein, atomic layer deposition (ALD) introduced ultrathin blocking layers (BLs) between a mesoporous TiO2 membrane and fluorine-doped tin oxide (FTO), and much improved photoelectrochemical water oxidation performance was well documented. Samples with different BL thicknesses deposited on FTO were obtained by ALD. In the photoanode, polypyridyl Ru(II) complexes were used as photosensitizers, and Ru(bda)-type was used as a catalyst during water oxidation. Under one sun irradiation, the BL (i) increased the photocurrent density; (ii) slowed down the open-circuit voltage decay (OCVD) by electrochemical measurement; (iii) increased the photo-generated electron lifetime roughly from 1 s to more than 100 s; and (iv) enhanced the water oxidation efficiency from 25% to 85% with 0.4 V of applied voltage bias. All this pointed out that the ALD technique-prepared layers could greatly hinder the photogenerated electron–hole pair recombination in the TiO2-based photoanode. This study offers critical backing for the building of molecular films by the ALD technique to split water effectively.

Temperature-Controlled Transformation of WO3 Nanowires into Active Facets-Exposed Hexagonal Prisms toward Efficient Visible-Light-Driven Water Oxidation.

A unique transformation of WO3 nanowires (NW-WO3) into hexagonal prisms (HP-WO3) was demonstrated by tuning the temperature of the (N2H4)WO3 precursor suspension prepared from tungstic acid and hydrazine as a structure-directing agent. The precursor preparation at 20 °C followed by calcination at 550 °C produced NW-WO3 nanocrystals (ca. <100 nm width, 3-5 μm length) with anisotropic growth of monoclinic WO3 crystals to (002) and (200) planes and a polycrystalline character with randomly oriented crystallites in the lateral face of nanowires. The precursor preparation at 45 °C followed by calcination at 550 °C produced HP-WO3 nanocrystals (ca. 500-1000 nm diameter) with preferentially exposed (002) and (020) facets on the top-flat and side-rectangle surfaces, respectively, of hexagonal prismatic WO3 nanocrystals with a single-crystalline character. The HP-WO3 electrode exhibited the superior photoelectrochemical (PEC) performance for visible-light-driven water oxidation to that for the NW-WO3 electrode; the incident photon-to-current conversion efficiency (IPCE) of 47% at 420 nm and 1.23 V vs RHE for HP-WO3 was 3.1-fold higher than 15% for the NW-WO3 electrode. PEC impedance data revealed that the bulk electron transport through the NW-WO3 layer with the unidirectional nanowire structure is more efficient than that through the HP-WO3 layer with the hexagonal prismatic structure. However, the water oxidation reaction at the surface for the HP-WO3 electrode is more efficient than the NW-WO3 electrode, contributing significantly to the superior PEC water oxidation performance observed for the HP-WO3 electrode. The efficient water oxidation reaction at the surface for the HP-WO3 electrode was explained by the high surface fraction of the active (002) facet with fewer grain boundaries and defects on the surface of HP-WO3 to suppress the electron-hole recombination at the surface.

Interfacial properties of Co3O4/Gd–Fe2O3 p-n junction photoanode improved by PDDA functional layer for efficient photoelectrochemical water oxidation

The phase interface properties of the p-n junction may profoundly affect its photoelectrochemical (PEC) water oxidation performance. Here, we introduced a non-conjugated polymer functional layer (poly(diallyl-dimethylammonium chloride, PDDA) between the interfaces of the p-n junction (Co3O4/Gd–Fe2O3) to tune the interfacial properties. First, the PDDA modulates the band structure so that the composite photoanode (Co3O4/PDDA/Gd–Fe2O3) has an enlarger band bending than the p-n junction. Then, PDDA passivates the surface trap, which synergizes with Co3O4 to provide more active sites for water oxidation. Furthermore, PDDA improves the PEC water oxidation kinetics. Specifically, PDDA extracts holes and adsorbs water oxidation reactants, thus it efficiently transfers photogenerated holes to Co3O4, promoting the water oxidation reaction in the positive direction. With these positive modulations, PDDA can further enhance the PEC water oxidation performance of the p-n junction. This conceptual work provides insight into the role of the non-conjugated polymer in PEC water splitting.

Revealing the enhanced photoelectrochemical water oxidation activity of Fe-based metal-organic polymer-modified BiVO4 photoanode

Metal-organic polymers (MOPs) can enhance the photoelectrochemical (PEC) water oxidation performance of BiVO4 photoanodes, but their PEC mechanisms have yet to be comprehended. In this work, we constructed an active and stable composite photoelectrode by overlaying a uniform MOP on the BiVO4 surface using Fe2+ as the metal ions and 2,5-dihydroxyterephthalic acid (DHTA) as ligand. Such modification on the BiVO4 surface yielded a core-shell structure that could effectively enhance the PEC water oxidation activity of the BiVO4 photoanode. Our intensity-modulated photocurrent spectroscopy analysis revealed that the MOP overlayer could concurrently reduce the surface charge recombination rate constant (ksr) and enhance the charge transfer rate constant (ktr), thus accelerating water oxidation activity. These phenomena can be ascribed to the passivation of the surface that inhibits the recombination of the charge carrier and the MOP catalytic layer that improves the hole transfer. Our rate law analysis also demonstrated that the MOP coverage shifted the reaction order of the BiVO4 photoanode from the third-order to the first-order, resulting in a more favorable rate-determining step where only one hole accumulation is required to overcome water oxidation. This work provides new insights into the reaction mechanism of MOP-modified semiconductor photoanodes.