Charge Recombination Reactions Research Articles

Stacked High‐Entropy Hydroxides Promote Charge Transfer Kinetics for Photoelectrochemical Water Splitting

AbstractAlthough various kinds of cocatalyst are developed and decorated on the bismuth vanadate (BiVO4) photoanode, its photoelectrochemical (PEC) water splitting performance is limited owing to severe charge recombination and sluggish oxygen evolution reaction (OER). Herein, a high‐entropy hydroxide electrocatalyst (FeCoNiMoCrOOH) is constructed as a co‐catalyst deposited on BiVO4 with a good PEC activity and stability in potassium borate buffer, addressing substantial charge recombination and poor surface oxygen evolution reaction of the material. FeCoNiMoCrOOH synthesized by a simple electrodeposition stacking strategy, delivers an overpotential of 172 mV at 10 mA cm−2 with a stability of 600 h under alkaline conditions, representing one of the best performances on high‐entropy‐based catalysts. The FeCoNiMoCrOOH/BiVO4 photoanode shows a photocurrent density of 5.23 mA cm−2 at 1.23 VRHE with 100 h durability in potassium borate buffer. Experimental investigations and theoretical calculations demonstrate that the synergistic effect of Mo and Cr in FeCoNi catalyst effectively decreases the dissolution Fe, Co, and Ni after long‐term operation, increases the charge transfer kinetics, and promotes OER and PEC performances, therefore enhancing the photocorrosion resistance of BiVO4. This work provides a new avenue to design high entropy‐based electrocatalysts boosting solar water splitting activity and stability.

Quasi-type-II Cu-In-Zn-S/Ni-MOF heterostructure with prolonged carrier lifetime for photocatalytic hydrogen production

Visible-driven photocatalytic hydrogen production using narrow-bandgap semiconductors has great potential for clean energy development. However, the widespread use of these semiconductors is limited due to problems such as severe charge recombination and slow surface reactions. Herein, a quasi-type-II heterostructure was constructed by combining bifunctional Ni-based metal–organic framework (Ni-MOF) nanosheets with BDC (1,4-benzenedicarboxylic acid) linker coupled with Cu-In-Zn-S quantum dots (CIZS QDs). This heterostructure exhibited a prolonged charge carrier lifetime and abundant active sites, leading to significantly improved hydrogen production rate. The optimized rate achieved by the CIZS/Ni-MOF heterostructure was 2642 μmol g−1 h−1, which is 5.28 times higher than that of the CIZS QDs. This improved performance can be attributed to the quasi-type-II band alignment between the CIZS QDs and Ni-MOF, which facilitates effective delocalization of the photogenerated electrons within the system. Additional photoelectrochemical tests confirmed the well-maintained photoluminescence and prolonged charge carrier lifetime of the CIZS/Ni-MOF heterostructure. This study provides valuable insights into the use of multifunctional MOFs in the development of highly efficient composite photocatalysts, extending beyond their role in light harvesting and charge separation.

MoO3/BiVO4 heterojunction modified with cobalt-manganese layered double hydroxide cocatalyst for photoelectrochemical water oxidation

To improve the charge recombination and poor oxygen evolution reaction (OER) kinetics of BiVO4, in this paper, a high-performance CoMn-LDH/MoO3/BiVO4 photoanode was synthesized by a simple electrodeposition and calcination method. CoMn-LDH/MoO3/BiVO4 shows a photocurrent density of 3.78 mA cm−2 at 1.23 V vs. RHE, which is 3.78 times higher than that of pure BiVO4 with negative shift onset potentials of 330 mV. The maximum applied bias photon-to-current efficiency (ABPE) and incident photon-to-current conversion efficiency (IPCE) are 1.24 % and 55.5 %, respectively, which are 13.8 and 12.5 times higher than those of pure BiVO4. In-depth studies demonstrate that the MoO3/BiVO4 heterojunction can better drive the transfer of photogenerated carriers and suppress bulk charge recombination, CoMn-LDH improves the OER kinetics and broadens the absorption of visible light, their synergistic effect significantly enhances charge separation and light harvesting of BiVO4. This work provides a facile electrodeposition method to fabricate highly efficient photoanodes for solar-driven water splitting.

Surface Engineering of GaN Photoelectrode by NH3 Treatment for Solar Water Oxidation

<p>Photoelectrochemical (PEC) water splitting is a vital source of clean and sustainable hydrogen energy. Moreover, the largescale H<sub>2</sub> production is currently necessary, while long-term stability and high PEC activity still remain important issues. In this study, a GaN-based photoelectrode was modified by an additional NH<sub>3</sub> treatment (900°C for 10 min) and its PEC behavior was monitored. The bare GaN exhibited a highly crystalline wurtzite structure with the (002) plane and the optical bandgap was approximately 3.2 eV. In comparison, the NH<sub>3</sub>-treated GaN film exhibited slightly reduced crystallinity and a small improvement in light absorption, resulting from the lattice stress or cracks induced by the excessive N supply. The minor surface nanotexturing created more surface area, providing electroactive reacting sites. From the surface XPS analysis, the formation of an N-Ga-O phase on the surface region of the GaN film was confirmed, which suppressed the charge recombination process and the positive shift of E<sub>FB</sub>. Therefore, these effects boosted the PEC activity of the NH<sub>3</sub>-treated GaN film, with <italic>J</italic> values of approximately 0.35 and 0.78 mA·cm<sup>−2</sup> at 0.0 and 1.23 V<sub>RHE</sub>, respectively, and an onset potential (V<sub>on</sub>) of −0.24 V<sub>RHE</sub>. In addition, there was an approximate 50% improvement in the <italic>J</italic> value within the highly applied potential region with a positive shift of V<sub>on</sub>. This result could be explained by the increased nanotexturing on the surface structure, the newly formed defect/trap states correlated to the positive V<sub>on</sub> shift, and the formation of a GaO<sub>x</sub>N<sub>1-x</sub> phase, which partially blocked the charge recombination reaction.</p>

(Invited) Z-Scheme Water Splitting Using Dye-Sensitized Metal Oxide Nanosheets

Solar water splitting by a heterogeneous photocatalyst, producing H2 and O2, is a potential solution for realizing large-scale H2 production. While dye-sensitized metal oxides are good candidates as H2 evolution photocatalysts for solar-driven Z-scheme water splitting, their solar-to-hydrogen (STH) energy conversion efficiencies remains low because of uncontrolled charge recombination reactions. Here it is shown that modification of Ru dye-sensitized, Pt- intercalated HCa2Nb3O10 nanosheets (Ru/Pt/HCa2Nb3O10) with both amorphous Al2O3 and poly(styrenesulfonate) (PSS) improves the STH efficiency of Z-scheme overall water splitting by a factor of ~100, when the nanosheets are used in combination with a WO3-based O2 evolution photocatalyst and an I3 –/I– redox mediator, relative to an analogous system that uses unmodified Ru/Pt/HCa2Nb3O10. The Al2O3 and PSS modifiers, which have previously been shown to suppress back electron transfer reactions in a dye-sensitized H2 evolution photocatalyst, enabled operation of the Z-scheme system even at low intensity of simulated sunlight without a decrease in the STH values. By using the optimized photocatalyst, PSS/Ru/Al2O3/Pt/HCa2Nb3O10, a maximum STH of 0.12% and an apparent quantum yield of 4.1% at 420 nm were obtained, by far the highest among dye-sensitized water splitting systems and also comparable to conventional semiconductor-based suspended particulate photocatalyst systems.

Charge separation via synergy of homojunction and electrocatalyst in BiVO4 for photoelectrochemical water splitting

Bismuth vanadate (BiVO4) as oxygen evolution photoanodes in photoelectrochemical (PEC) water splitting is hampered by the severe charge recombination and sluggish kinetic reaction. Herein, we successively construct a novel homogenous BVO/BiVO4 photoanodes consisting of BiVO4 nanodots (BVO) with exposed (011) crystal facet on BiVO4 substrate that did not only creates tunable (011)/(110) crystal planes upon homogeneous interfacial contact but also demonstrates an unprecedented photocurrent density with outstanding performance. Theoretical calculations clearly reveal that the tunable (011)/(110) crystal facet facilitates the charge separation efficiency and water splitting kinetics. Furthermore, the photocurrent density of the homogenous BVO/BiVO4 is further enhanced by additional photo-deposition of NiFeOx electrocatalyst layer (denoted NiFeOx/BVO/BiVO4). Consequently, the optimized NiFeOx/BVO/BiVO4 photoanodes not only reaches an unprecedented photocurrent density of 6.40 mA cm−2 at 1.23 V versus reversible hydrogen electrode (RHE) under simulated AM 1.5G illumination, but also generates an outstanding durability. This work endows a new environmentally friendly and effective path for improving PEC water splitting of BiVO4 photoanodes.

Excited State Processes in Supramolecular Complexes of Cyclic Dibenzopyrrolopyrrole Isomers with C60 Fullerene.

An approach to modulating the properties of carbon nanorings by incorporating pyrrolo[3,2-b]pyrrole units is of particular interest due to the combined effect of heteroatom and antiaromatic character on electronic properties. The inclusion of units other than phenylene leads to the formation of stereoisomers. In this work, we computationally study how the spatial orientation of monomeric units in the ring affects the properties of cyclic dibenzopyrrolo[3,2-b]pyrroles and their complexes with C60 fullerene. For [4]PP and [4]DHPP, the most symmetrical AAAA isomer is the most stable and forms stronger interactions with fullerene than the isomers where one or two monomeric units are flipped, mostly due to less Pauli repulsion. π-Electron delocalization in the monomeric unit is crucial for directing the electron transfer (from or to nanoring). The energy of excited states with charge transfer depends on the HOMO-LUMO gap, which varies from one stereoisomer to another only for [4]DHPP⊃C60 with aromatic 1,4-dihydropyrrolo[3,2-b]pyrrole units. The rates of electron transfer and charge recombination reactions are relatively weakly dependent of the spatial isomerism of nanorings.

Non-noble-metal CuSe promotes charge separation and photocatalytic CO2 reduction on porous g-C3N4 nanosheets

Photocatalytic CO2 reduction based on g-C3N4 with inexpensive, efficient, stable, and suitable energy band structure, serve as a promising candidate for alleviating the greenhouse effect. However, g-C3N4 still suffers from low CO2 photoreduction performance owing to severe charge recombination and high surface reaction energy barriers. Herein, porous g-C3N4/CuSe (PCN/CS) Schottky heterojunctions were fabricated by loading non-precious CS nanosheets on porous PCN nanosheets, contributing to a decreased the reaction energy barrier and elevated charge separation. The improved charge separation by Schottky heterojunction were unveiled by the transient photocurrents as well as photoluminescence (PL) spectra. The photogenerated electrons transfer from PCN to CS was demonstrated by density functional theory (DFT) calculations and XPS analysis. Meanwhile, CS lowers the energy berries and serves as an active site for CO2 reduction, thus accelerating the CO2 photoreduction processes. The experimental results manifest that the CO2 photoreduction efficiency of PCN/CS was significantly higher than that of pure PCN and CS. The efficiency of CO2 photoreduction to CO in the composite sample was 25.03 μmol·g−1·h−1, which was 6.53 times and 2.45 times higher than that of pure CS and PCN, respectively. This work provides a new insight on the design of Schottky junctions by anchoring non-precious metal on PCN for ameliorated CO2 photoreduction performance.

Spatially Separated Redox Cocatalysts on Ferroelectric Nanoplates for Improved Piezophotocatalytic CO2 Reduction and H2O Oxidation.

Utilizing solar and mechanical vibration energy for catalytic CO2 reduction and H2O oxidation is emerging as a promising way to simultaneously generate renewable energy and mitigate climate change, making it possible to integrate two energy resources into a reaction system for artificial piezophotosynthesis. However, the practical applications are hindered by undesirable charge recombination and sluggish surface reaction in the photocatalytic and piezocatalytic processes. This study proposes a dual cocatalyst strategy to overcome these obstacles and improve the piezophotocatalytic performance of ferroelectrics in overall redox reactions. With the photodeposition of AuCu reduction and MnOx oxidation cocatalysts on oppositely poled facets of PbTiO3 nanoplates, band bending occurs along with the formation of built-in electric fields on the semiconductor-cocatalyst interfaces, which, together with an intrinsic ferroelectric field, piezoelectric polarization field, and band tilting in the bulk of PbTiO3, provide strong driving forces for the directional drift of piezo- and photogenerated electrons and holes toward AuCu and MnOx, respectively. Besides, AuCu and MnOx enrich the active sites for surface reactions, significantly reducing the rate-determining barrier for CO2-to-CO and H2O-to-O2 transformation, respectively. Benefiting from these features, AuCu/PbTiO3/MnOx delivers remarkably improved charge separation efficiencies and significantly enhanced piezophotocatalytic activities in CO and O2 generation. This strategy opens a door for the better coupling of photocatalysis and piezocatalysis to promote the conversion of CO2 with H2O.

Direct In Situ Measurement of Quantum Efficiencies of Charge Separation and Proton Reduction at TiO2-Protected GaP Photocathodes.

Photoelectrochemical solar fuel generation at the semiconductor/liquid interface consists of multiple elementary steps, including charge separation, recombination, and catalytic reactions. While the overall incident light-to-current conversion efficiency (IPCE) can be readily measured, identifying the microscopic efficiency loss processes remains difficult. Here, we report simultaneous in situ transient photocurrent and transient reflectance spectroscopy (TRS) measurements of titanium dioxide-protected gallium phosphide photocathodes for water reduction in photoelectrochemical cells. Transient reflectance spectroscopy enables the direct probe of the separated charge carriers responsible for water reduction to follow their kinetics. Comparison with transient photocurrent measurement allows the direct probe of the initial charge separation quantum efficiency (ϕCS) and provides support for a transient photocurrent model that divides IPCE into the product of quantum efficiencies of light absorption (ϕabs), charge separation (ϕCS), and photoreduction (ϕred), i.e., IPCE = ϕabsϕCSϕred. Our study shows that there are two general key loss pathways: recombination within the bulk GaP that reduces ϕCS and interfacial recombination at the junction that decreases ϕred. Although both loss pathways can be reduced at a more negative applied bias, for GaP/TiO2, the initial charge separation loss is the key efficiency limiting factor. Our combined transient reflectance and photocurrent study provides a time-resolved view of microscopic steps involved in the overall light-to-current conversion process and provides detailed insights into the main loss pathways of the photoelectrochemical system.

Acceleration of Nonradiative Charge Recombination Reactions at Larger Distances in Kinked Donor-Bridge-Acceptor Molecules.

Photoinduced electron transfer in donor-bridge-acceptor (D-B-A) molecular systems can occur via tunneling over long distances (rDA) of well over 10 Å. We commonly observe decreasing rates of electron transfer with increasing distances, a result of a decrease in the electronic coupling of the donor and acceptor moiety. In the study of D-B-A molecules with Ru(bpy)32+ as a bridge/core, Kuss-Petermann and Wenger observed the opposite trend (J. Am. Chem. Soc.2016, 138, 1349); a maximum rate constant of electron transfer was observed at an intermediate electron transfer distance. Within the high-temperature limit of the classical Marcus equation, their observation was qualitatively explained by a sharp distance dependence of outer sphere (or solvent) reorganization energy, as predicted by Sutin and co-workers (J. Am. Chem. Soc.1984, 106, 6858), and almost distance-independent electronic couplings. Here, we report another example of such an underexplored behavior with three kinked D-B-A systems of rDA ∼ 10-19 Å, showing increasing rates of nonradiative charge recombination with increasing rDA. The three D-B-A systems are based on boron dipyrromethene and triphenylamine as electron acceptor and donor groups, respectively, with aryl bridges where the donor and acceptor moieties are connected at meso-positions. These D-B-A molecules exhibit radiative electron transfer reactions (or charge-transfer emission), which enables us to experimentally determine the solvent reorganization energy and the electronic couplings. The analysis of charge-transfer emission that explicitly considers electron-vibration coupling, in conjunction with the temperature-dependent analysis and computational method, revealed that the solvent reorganization energy indeed increases with distance, and at the same time, the electronic coupling decreases with distance expectedly. Therefore, under the right conditions for solvent reorganization energy and electronic coupling values, our results show that we can observe the acceleration of electron transfer reactions with increasing distance, even when we have the expected distance dependence of electronic coupling. This work indicates that the acceleration of electron transfer with increasing distance may be achieved with a fine-tuning of molecular design.

Singlet oxygen production by photosystem II is caused by misses of the oxygen evolving complex.

Singlet oxygen (1 O2 ) is a harmful species that functions also as a signaling molecule. In chloroplasts, 1 O2 is produced via charge recombination reactions in photosystem II, but which recombination pathway(s) produce triplet Chl and 1 O2 remains open. Furthermore, the role of 1 O2 in photoinhibition is not clear. We compared temperature dependences of 1 O2 production, photoinhibition, and recombination pathways. 1 O2 production by pumpkin thylakoids increased from -2 to +35°C, ruling out recombination of the primary charge pair as a main contributor. S2 QA - or S2 QB - recombination pathways, in turn, had too steep temperature dependences. Instead, the temperature dependence of 1 O2 production matched that of misses (failures of the oxygen (O2 ) evolving complex to advance an S-state). Photoinhibition in vitro and in vivo (also in Synechocystis), and in the presence or absence of O2 , had the same temperature dependence, but ultraviolet (UV)-radiation-caused photoinhibition showed a weaker temperature response. We suggest that the miss-associated recombination of P680 + QA - is the main producer of 1 O2 . Our results indicate three parallel photoinhibition mechanisms. The manganese mechanism dominates in UV radiation but also functions in white light. Mechanisms that depend on light absorption by Chls, having 1 O2 or long-lived P680 + as damaging agents, dominate in red light.

Construction of highly active WO3/TpPa-1-COF S-scheme heterojunction toward photocatalytic H2 generation

• WO 3 /TpPa-1-COF is synthesized through an in-situ growth approach. • Internal electric field drives the charge carrier diffusion in S-scheme mode. • WO 3 /TpPa-1-COF has strong redox abilities and high charge separation efficiency. • WO 3 /TpPa-1-COF display superior photocatalytic H 2 generation performance. The rapid charge recombination and low surface reaction kinetics are the two major constraints to the photocatalytic performance of covalent organic frameworks (COFs). To accelerate the charge separation behavior, TpPa-1-COF is decorated with WO 3 via an in-situ growth approach, and the resultant WO 3 /TpPa-1-COF composites show significantly improved photocatalytic performance. Especially, when the WO 3 loading arrives at 3 wt%, 3%WO 3 /TpPa-1-COF exhibits the maximum photocatalytic H 2 evolution rate of 19.89 mmol g −1 h −1 , which is approximately 4.8 times higher than that of pure TpPa-1-COF. The apparent quantum efficiency (AQE) of 3%WO 3 /TpPa-1-COF at 420 nm is detected to be 12.4%. X-ray photoelectron spectroscopy (XPS) characterization confirms the formation of internal electric field between WO 3 and TpPa-1-CF, which can drive the photogenerated charge carrier diffusion in S-scheme mode. As a result, WO 3 /TpPa-1-COF composite possesses high charge separation efficiency and strong redox ability, which is further supported by the photoelectrochemical results, thus benefiting the photocatalysis process. This work provides a rational strategy to modify COFs in photocatalytic water splitting.

Small Molecules Containing Amphoteric Imidazole Motifs as Sensitizers for Dye-Sensitized Solar Cells: An Overview.

Organic dyes, porphyrins and inorganic complexes containing imidazole (IM) motifs have been demonstrated as a new class of sensitizers in dye-sensitized solar cells (DSSCs). Particularly, the amphoteric nature of IM-based motifs allows them to be used as donors (D), auxiliary donors (DA), linker/branch (π), or acceptors (A) in D-π-A-based organic dyes and porphyrins and also employed as cyclometalated heteroleptic and ancillary ligands in the Ru(II) and Ir(III) complexes for DSSCs. It is noteworthy that the introduction of IM chromophores in the dyes of D-π-A configuration can improve the light-harvesting properties and prohibit the charge recombination reactions due to the extension of the π-conjugated structures and hydrophobic nature. Similarly, in the case of inorganic complexes, the presence of IM motifs as ligands can improve the light-harvesting ability, give facilely tuned HOMO and LUMO energy levels, increase the charge recombination resistance and photostability. This results in enhanced photocurrent (JSC) and photovoltage (VOC) and consequently solar-to-power conversion efficiency (η) of DSSC devices based on Ru(II) and Ir(III) complexes. Considering the interesting DSSC applications of IM-derived molecules, in this review, we therefore comprehensively discuss their photophysical, electrochemical and photovoltaic properties reported so far and establish their structure-activity relationship to further advance the η of DSSCs. To the best of our knowledge, there is no such a review interpreting the importance of molecules possessing IM-motifs for DSSC applications to date.

In-situ assembling 0D/2D Z-scheme heterojunction of Lead-free Cs2AgBiBr6/Bi2WO6 for enhanced photocatalytic CO2 reduction

All-inorganic lead-free halide double perovskites have emerged as rising star photocatalysts to substitute the toxic lead-based hailed perovskites (LHPs) owing to their unique photophysical properties. Nevertheless, their photocatalytic activities toward CO2 reduction are still far from comparable with the LHPs, associated with severe charge recombination and sluggish surface catalytic reaction. Herein, a delicate 0D/2D heterojunction of Cs2AgBiBr6/Bi2WO6 (CABB/BWO) was assembled by in-situ growing cubic CABB nanocrystals on the flat surface of BWO nanosheets via a facile hot-injection method. Density functional theory (DFT) calculations disclose that the work function and Fermi level difference between CABB and BWO give rise to charge redistribution at the interface upon the formation of the heterojunction, creating an internal electric field (IEF). Upon light irradiation, the IEF enables the photogenerated electron transfer from BWO to CABB via direct Z-scheme electron transfer mode with striking spatial charge separation as verified by in-situ X-ray photoelectron (XPS) and electron spin resonance (ESR) spectra. Consequently, the CABB/BWO heterojunction realizes 7-fold higher photocatalytic activity than pristine CABB with significant electron consumption rate of 87.66 µmol g-1h−1 under simulated solar light (AM 1.5G).

Surface-modified, dye-sensitized niobate nanosheets enabling an efficient solar-driven Z-scheme for overall water splitting.

While dye-sensitized metal oxides are good candidates as H2 evolution photocatalysts for solar-driven Z-scheme water splitting, their solar-to-hydrogen (STH) energy conversion efficiencies remain low because of uncontrolled charge recombination reactions. Here, we show that modification of Ru dye–sensitized, Pt-intercalated HCa2Nb3O10 nanosheets (Ru/Pt/HCa2Nb3O10) with both amorphous Al2O3 and poly(styrenesulfonate) (PSS) improves the STH efficiency of Z-scheme overall water splitting by a factor of ~100, when the nanosheets are used in combination with a WO3-based O2 evolution photocatalyst and an I3−/I− redox mediator, relative to an analogous system that uses unmodified Ru/Pt/HCa2Nb3O10. By using the optimized photocatalyst, PSS/Ru/Al2O3/Pt/HCa2Nb3O10, a maximum STH of 0.12% and an apparent quantum yield of 4.1% at 420 nm were obtained, by far the highest among dye-sensitized water splitting systems and comparable to conventional semiconductor-based suspended particulate photocatalyst systems.

Roles of Cocatalysts on BiVO4 Photoanodes for Photoelectrochemical Water Oxidation: A Minireview

Photoelectrochemical (PEC) water splitting is regarded as a promising approach to solve the energy crisis by converting solar energy into hydrogen. The development of effective photoelectrodes is of important to increase the solar-to-hydrogen conversion efficiency for practical application. Bismuth vanadate (BiVO4) is an outstanding photoanode material because of its relatively narrow band gap, suitable valence band position, and nontoxicity. However, severe charge recombination and slow reaction kinetics limit its PEC performance in the water splitting reaction. Loading cocatalysts on BiVO4 photoanodes has become an important and effective method to enhance PEC water oxidation performance. In this review, we summarize recent important works in coupling a cocatalyst with BiVO4 photoanodes for PEC water splitting reactions. Finally, the foremost challenges and some motivating prospects for future research on coupling cocatalysts with BiVO4 photoanodes materials are presented.

Boosting the Photocatalytic H2 Evolution and Benzylamine Oxidation using 2D/1D g-C3N4/TiO2 Nanoheterojunction.

The present research aims at the elevation of solar-to-chemical energy conversion with extortionate performance and sustainability. The nanostructured materials are revolutionizing the water splitting technology into decoupled hydrogen with simultaneous value-added organic chemical production. Yet, the bottleneck in semiconductor photocatalysis is rapid charge recombination and sluggish reaction kinetics. Herein, we demonstrate an efficient and non-noble metal-based catalyst for successful redox reaction with a theoretical modeling through density functional theory (DFT) study. Implementing this robust approach on 2D/1D ultrathin g-C3N4 nanosheets and TiO2 nanowires heterojunction, we achieved H2 production of 5.1 mmol g-1 h-1 with apparent quantum efficiency of 7.8% under visible light illumination and 93% of benzylamine conversion to N-benzylidene benzylamine in situ. The interface of 2D g-C3N4 nanosheets and 1D nanowires provide ample active sites and extends the visible light absorption with requisite band edge position for the separation of photoinduced charge carriers with superior stability. The electronic properties, band structure, and stability of the heterojunction are further investigated via DFT calculations which corroborate the experimental results and in good agreement for the enhanced activity of the heterojunction.

Hierarchical mesoporous SnO2/BiVO4 photoanode decorated with Ag nanorods for efficient photoelectrochemical water splitting

Bismuth vanadate has been extensively investigated as a potential visible light photoanode for PEC water splitting. The performance of BiVO4 is restricted by fast charge recombination and slow oxygen evolution reaction kinetic. To address these issues, hierarchical SnO2 (HSN) mesoporous support is developed via a novel sol-electrophoretic approach, and BiVO4 film is decorated with silver nanorods (Ag NRs). The photocurrent density of HSN/BiVO4 photoanode is 3.98 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) and onset potential (Vonset) of 0.5 V vs. RHE. The PEC performance is attributed to the appropriate band alignment between SnO2 and BiVO4, as well as the hierarchical structure of SnO2. Ag-HSN/BiVO4 photoanode shows photocurrent density of 4.30 mA/cm2 at 1.23 V vs. RHE and Vonset of 0.28 V vs. RHE. The enhanced photocurrent and negatively shifted Vonset can be attributed to radiative localized surface plasmon resonance decay and catalytic effect of Ag NRs, respectively.

Spatial Separation of Cocatalysts on Z-Scheme Organic/Inorganic Heterostructure Hollow Spheres for Enhanced Photocatalytic H2 Evolution and In-Depth Analysis of the Charge-Transfer Mechanism.

A Z-scheme heterojunction with spatially separated cocatalysts is proposed for overcoming fundamental issues in photocatalytic water splitting, such as inefficient light absorption, charge recombination, and sluggish reaction kinetics. For efficient light absorption and interfacial charge separation, Z-scheme organic/inorganic heterojunction photocatalysts are synthesized by firmly immobilizing ultrathin g-C3 N4 on the surface of TiO2 hollow spheres via electrostatic interactions. Additionally, two cocatalysts, Pt and IrOx , are spatially separated along the Z-scheme charge-transfer pathway to enhance surface charge separation and reaction kinetics. The as-prepared Pt/g-C3 N4 /TiO2 /IrOx (PCTI) hollow sphere photocatalyst exhibits an exceptional H2 evolution rate of 8.15mmol h-1 g-1 and a remarkable apparent quantum yield of 24.3% at 330nm in the presence of 0.5 wt% Pt and 1.2 wt% IrOx cocatalysts on g-C3 N4 and TiO2 , respectively. Photoassisted Kelvin probe force microscopy is used to systematically analyze the Z-scheme charge-transfer mechanism within PCTI. Furthermore, the benefits of spatially separating cocatalysts in the PCTI system are methodically investigated in comparison to randomly depositing them. This work adequately demonstrates that the combination of a Z-scheme heterojunction and spatially separated cocatalysts can be a promising strategy for designing high-performance photocatalytic platforms for solar fuel production.