Performance Of Photoanodes Research Articles

Nano-Structured InGaN Photoanode for Hydrogen Production Using Photoelectrochemical Water Splitting: A Simulation Study

Abstract InGaN nanostructures have emerged as a promising solution for developing efficient and stable photoelectrodes for hydrogen production using photoelectrochemical (PEC) water splitting. In this work, we investigate the performance of an InGaN nanopyramid photoanode through electrical and optical simulations. The simulated structure consists of a p-GaN/InGaN NP /n-GaN nanopyramid with 12 pairs of TiO2/SiO2 dielectric Bragg reflector. We obtain a short-circuit current and a power density of 12.23 mA/cm2 and 16 mW/cm2, respectively. We also compare the photoelectrochemical properties of the InGaN nanopyramid photoanode and a planar InGaN photoanode. The incident photon conversion efficiency of the InGaN nanopyramid reaches 43% compared to 9.5% in the case of planar InGaN photoanode. The hydrogen evolution rate of the InGaN NP reaches 228 µmol.cm-2.h-1, which is four times higher than the planar InGaN photoanode. As for solar-to-hydrogen efficiency, we obtained 15% and 3% for InGaN nanopyramid and planar InGaN photoanode, respectively. Our results suggest that InGaN nanopyramids can serve as an efficient photoanode to produce hydrogen gas via PEC water splitting.

Enhancement of photoelectrochemical water splitting performance of TiO2 photoanodes via synergistic hole separation and transfer of Ferrihydrite/CoOOH functional layer

Enhancement of photoelectrochemical water splitting performance of TiO2 photoanodes via synergistic hole separation and transfer of Ferrihydrite/CoOOH functional layer

Surface Nd Sites Boost Charge Transfer of Fe2O3 Photoanodes for Enhanced Solar Water Oxidation.

Photoelectrochemical (PEC) water splitting for hydrogen production is a promising technology for sustainable energy generation. In this work, we introduce Nd sites boost the PEC performance of Fe2O3 photoanodes through a precise gas-phase cation exchange process, which substitutes surface Fe atoms with Nd. The incorporation of Nd significantly enhances charge transfer properties, increases carrier concentration, and reduces internal resistance, leading to a substantial increase in photocurrent density from 0.44 to 0.92 mA cm-2 at 1.23 VRHE. Further enhancement of catalytic activity was achieved by depositing a NiCo(OH)x layer and a photocurrent density of 1.15 mA cm-2 at 1.23 VRHE were obtained. Theoretical calculations corroborate these experimental results, revealing that Nd doping narrows the bandgap, improves charge separation efficiency, and lowers the reaction potential barrier, thereby accelerating water oxidation kinetics. These findings underscore the effectiveness of surface cation exchange and targeted metallic element doping in overcoming the intrinsic limitations of Fe2O3, providing a viable pathway for developing high-performance PEC systems for efficient hydrogen production.

Insight into Charge Transport Behaviors in Hematite Photoanodes via Potential-Dependent Impedance Spectroscopy and Machine Learning.

We employed machine learning (ML) techniques combined with potential-dependent photoelectrochemical impedance spectroscopy (pot-PEIS) to gain deeper insights into the charge transport mechanisms of hematite (α-Fe2O3) photoanodes. By the Shapley Additive exPlanations (SHAP) analysis from the ML model constructed from a small data set (dozens of samples) of electrical parameters obtained from pot-PEIS and the PEC performance, we identified the dominant factors influencing the electron transport to the back contact in the bulk and hole transfer to a solution at the hematite/electrolyte interface. The results revealed that shallow defect states significantly enhance electron transport, while deep defect states impede it, and also one of the surface states enhances the hole transfer to the electrolyte solution. The incorporation of a titanium dioxide underlayer had an effect to increase shallow defect states to promote electron transport and induce a new surface state to promote hole transfer. Cobalt phosphate cocatalyst improved charge separation, leading to enhance electron transport in the bulk, and the cocatalyst surface state promotes the hole transfer at the interface. The understanding of the band diagram based on the selected dominant descriptors provided critical insights into the electronic structure, elucidating the role of defect states and surface states in influencing the overall photoanode performance. This study showcases the potential of combining ML and pot-PEIS for material optimization.

Combining Cocatalyst and Oxygen Vacancy to Synergistically Improve Fe2O3 Photoelectrochemical Water Oxidation Performance

Considering the poor conductivity of Fe2O3 and the weak oxygen evolution reaction associated with it, surface hole accumulation leads to electron hole pair recombination, which inhibits the photoelectrochemical (PEC) performance of the Fe2O3 photoanode. Therefore, the key to improving the PEC water oxidation performance of the Fe2O3 photoanode is to take measures to improve the conductivity of Fe2O3 and accelerate the reaction kinetics of surface oxidation. In this work, the PEC performances of Fe2O3 photoanodes are synergistically improved by combining loaded an FeOOH cocatalyst and oxygen vacancy doping. Firstly, amorphous FeOOH layers are successfully prepared on Fe2O3 nanostructures through simple photoassisted electrodepositon. Then oxygen vacancies are introduced into FeOOH-Fe2O3 through plasma vacuum treatment, which reduces the content of Fe-O (OL) and Fe-OH (-OH), jointly promoting the generation of oxygen vacancies. Oxygen vacancy can increase the concentration of most carriers in Fe2O3 and form photo-induced charge traps, promoting the separation of electron holes and enhancing the conductivity of Fe2O3. The other parts of -OH act as oxygen evolution catalysts to reduce the reaction obstacle of water oxidation and promote the transfer of holes to the electrode/electrolyte interface. The performance of FeOOH-Fe2O3 after plasma vacuum treatment has been greatly improved, and the photocurrent density is about 1.9 times higher than that of the Fe2O3 photoanode. The improvement in the water oxidation performance of PEC is considered to be the synergistic effect of the cocatalyst and oxygen vacancy. All outstanding PEC response characteristics show that the modification of the cocatalyst and oxygen vacancy doping represent a favorable strategy for synergistically improving Fe2O3 photoanode performance.

Enhanced Performance of Particulate Oxynitride Photoanodes by Electron‐Collecting‐Oxide Array Insertion for Photoelectrochemical Water Oxidation

AbstractThe collection of photogenerated electrons is a bottleneck to the photoelectrochemical performance of particulate photoanodes. In this work, the electron‐conducting array insertion strategy is applied for the assembly of LaTiO2N and SrNbO2N particulate photoanodes, and the candidates of conductive arrays are expanded from rigid vertically grown ZnO nanorod arrays to multi‐directionally grown ZnO nanoparticle arrays. ZnO nanorod arrays and ZnO nanoparticle arrays were inserted via electrodepositing ZnO from Zn(NO3)2 aqueous solution and n‐butanolic solution, respectively. By inserting a ZnO nanoparticle array, the performance of the assembled LaTiO2N micron particulate photoanodes is improved by 2 orders of magnitude compared to the uninserted one, and the photocurrent at 1.23 VRHE reaches 4.53 mA cm−2, slightly higher than 4.03 mA cm−2 (of the one assembled with a ZnO nanorod array). On the other hand, the performance of SrNbO2N hundred‐nanometer particulate photoanodes assembled with ZnO nanoarrays are 6–11 times of the uninserted one, and the photocurrent at 1.23 VRHE of the one assembled with a ZnO nanoparticle array reaches 1.88 mA cm−2, significantly higher than 0.97 mA cm−2 (of the one assembled with a ZnO nanorod array).

Quantification of mobile charge carrier yield and transport lengths in ultrathin film light-trapping ZnFe2O4 photoanodes.

Zinc ferrite (ZnFe2O4, ZFO) has gained attention as a candidate material for photoelectrochemical water oxidation. However, champion devices have achieved photocurrents far below that predicted by its bandgap energy. Herein, strong optical interference is employed in compact ultrathin film (8-14 nm) Ti-doped ZFO films deposited on specular back reflectors to boost photoanode performance through enhanced light trapping, resulting in a roughly fourfold improvement in absorption as compared to films deposited on transparent substrates. The spatial charge carrier collection profile and wavelength-dependent photogeneration yield of mobile charge carriers was then extracted via spatial collection efficiency analysis based on optical and external quantum efficiency measurements. We demonstrate that despite the enhanced performance enabled by the light trapping structure, substantial recombination occurs for thin film ZFO photoanodes even within the space charge region of an ultrathin film photoanode. Furthermore, the excitation-wavelength-dependent yield of mobile charge carriers in ZFO is shown to be less than unity across the visible spectrum, ultimately limiting the attainable photocurrent density. These results explain the underperformance of ZFO as a photoanode material and suggest that reduction of the mobile charge carrier yield due to the existence of ligand field states is a dominant loss mechanism for metal-oxides containing Fe metal centers with open d-shell configuration.

A review of photoelectrochemical water oxidation using hematite photoanode

Background: The sun, as an abundant and renewable energy source, provides a sustainable alternative to fossil fuels, which contribute significantly to CO₂ emissions and global warming. With CO₂ emissions surpassing 35 billion tons in 2023, the need for clean energy solutions has become increasingly urgent. Solar energy utilization includes photoelectrochemical (PEC) water splitting, where hematite is widely recognized as an efficient photoanode material due to its availability, stability, and favorable band gap for visible light absorption. However, hematite faces challenges such as poor conductivity, surface recombination, and slow oxygen evolution reaction (OER) kinetics, which limit its performance. Methods: This review examines various strategies to enhance hematite photoanode performance for PEC water splitting. The study explores three key approaches: (1) using three-dimensional conductive substrates with high surface area to facilitate heterojunction formation, (2) doping with tetravalent metal ions (e.g., Ti⁴⁺) to improve conductivity and charge carrier density, and (3) integrating Bi₂WO₆ with hematite to enhance charge separation and photoelectrochemical efficiency. The hydrothermal method was applied for hematite fabrication due to its feasibility, cost-effectiveness, and scalability. Findings: The analysis highlights the effectiveness of each strategy in overcoming hematite’s inherent limitations. The use of 3D conductive substrates improves electron transport and surface reaction sites, while Ti⁴⁺ doping enhances charge carrier density and conductivity. Conclusion: Hematite remains a promising photoanode material for PEC water splitting, but its limitations must be addressed to maximize efficiency. The combination of 3D conductive substrates, metal ion doping, and Bi₂WO₆ integration has shown potential in improving hematite’s photoelectrochemical performance. Novelty/Originality of this article: This review provides a comprehensive analysis of hematite performance enhancement strategies, focusing on the synergistic effects of 3D conductive substrates, Ti⁴⁺ doping, and Bi₂WO₆ integration.

Boosted Photoelectrochemical Water Oxidation Performance with a Quaternary Heterostructure: CoFe2O4/MWCNT-Doped MIL-100(Fe)/TiO2

Cobalt ferrite (CoFe2O4) combined with multi-walled carbon nanotubes (MWCNTs) is an outstanding material regarding photoelectrochemical water oxidation (PEC-WO) because of its excellent catalytic properties and stability. On the other hand, surface imperfections in CoFe2O4 can cause band bending and surface Fermi level pinning, significantly reducing its PEC conversion efficiency. Heterostructure engineering is essential for achieving increased light-gathering capacity and charge separation efficiency for PEC-WO. In this study, a quaternary heterostructure of CoFe2O4/MWCNT-doped Metal–Organic Framework-100 (Iron), MIL-100(Fe)/Titanium Oxide (TiO2) was synthesized by using a combination of hydrothermal, solvothermal, and “dip and dry” techniques. Characterization results confirmed the formation of a structural network of MIL-100(Fe) on TiO2 surfaces, enhanced by the incorporation of MWCNTs during the hydrothermal reaction. Under 1 sun irradiation, the resultant quaternary heterostructure displayed a photocurrent density (Jph) of 3.70 mA cm−2 under free bias voltage, which is around 3.08 times more than that of pristine TiO2 photoanodes (Jph = 1.20 mA cm−2). This investigation highlights the advantages of the MIL-100(Fe) network in improving the solar PEC-WO performance of TiO2 photoanodes.

Monolithic Lead Halide Perovskite Based Photoanode with 9.16% Applied Bias Photon-to-Current Efficiency

The quest for sustainable hydrogen production through solar energy conversion has directed attention towards photoelectrochemical (PEC) cell water splitting, a promising avenue for hydrogen (H₂) generation. Traditional metal-oxide-based photoelectrodes such as TiO2 and WO3, despite their extensive study, fail to absorb visible light effectively and exhibit poor charge transport properties. In contrast, lead halide perovskites (LHPs) emerge as a superior alternative, endowed with exceptional optoelectronic properties that enhance the solar spectrum photoresponse, critical for the efficient utilization of solar energy in hydrogen production.This study focused on optimizing the photoanode materials by improving the intrinsic properties of LHPs through bandgap tuning and enhanced charge transfer to the oxygen evolution reaction (OER) catalyst. However, the operational stability of LHPs in PEC applications poses a formidable challenge, primarily due to vulnerability to moisture-induced degradation.Addressing the stability concerns, some researches about application of ultrathin Ni surface layers and the use of low-melting-point field metals for protective encapsulation are reported. However, these methods have shown limited success in preventing moisture-induced degradation. In response, this work proposes the innovative use of conductive carbon poweder (CCP) as a superior alternative for enhancing electrical connectivity and stability between LHP solar cells and the OER catalyst.Our findings reveal that CCP's superior conductivity facilitates efficient charge transfer from LHP-based solar cells to OER catalysts, maintaining negligible current and voltage loss. To optimize the LHP photoanode's performance, we focused on enhancing the individual efficiencies and stabilities of the PSC and OER catalyst components. For the PSC, we improved stability by integrating a smaller cation (methylammonium, MA) into the FAPbI3 (formamidinium, FA) lattice, thereby stabilizing the α-phase and enhancing hydrogen bonding. This modification was substantiated through various spectroscopic and X-ray diffraction. Meanwhile, the OER catalyst's efficiency was amplified by employing a 3D-structured NiFe on an Ni foil substrate, improving catalytic activity and stability through enhanced hole mobility and increased electrochemically active surface area.The integrated LHP photoanode demonstrated a notable onset potential of 0.56 V and a peak photocurrent density of 24.26 mA/cm² at 1.23 V vs RHE, achieving a 9.16% applied bias photon-to-current efficiency and sustained performance over 48 hours in a pH 14 aqueous solution under simulated solar illumination. This performance is attributed to the synergistic effect of the optimized PSC and OER catalyst, facilitated by CCP's efficient electrical connectivity.

(Invited) Morphology-Engineered Hematite for Addressing Short Hole-Diffusion Lengths

This study addresses challenges in photoelectrochemical (PEC) water oxidation on hematite photoanodes, with a focus on overcoming the limited hole diffusion length (~4 nm) and poor electrical properties. To achieve this, an efficient overlayer is integrated onto the branched structure, generating a highly porous architecture by leveraging additional reaction interfaces exploiting the Kirkendall effect. This phenomenon occurs during high-temperature annealing, particularly at the interface of the overlayer and Ti-FeOOH (hematite precursor), utilizing distinct diffusion rates of metal atoms. By introducing additional interfaces on the hematite precursor surface, porosity and pore size are effectively controlled, resulting in a highly nanoporous structure. Through morphological engineering, the overlayer facilitates heteroatom diffusion (doping) into the hematite lattice, thereby promoting facile charge transport. The overlayer material selection is guided by density functional theory calculations. The resulting optimized photoanode, combined with an efficient cocatalyst (NiFe(OH)x), exhibits a maximum photocurrent density of 5.1 mA cm-2 at 1.23 V vs. RHE, marking a 3.2-fold increase compared to the reference hematite photoanode. This enhancement is attributed to the highly nanoporous structure and optimal doping. Thus, this study represents a significant advancement in enhancing the PEC performance of hematite-based photoanodes for future applications.

Optimizing photoelectrocatalytic Efficiency: Synergistic activation of peroxymonosulfate by CuFeO2/BiVO4 composites for antibiotic removal

The BiVO4 photoanode and CuFeO2 materials were synthesized via electrodeposition and hydrothermal methods, respectively, and the p-n type 2-CBVO (CuFeO2/BiVO4) composite photoanode was prepared using a spin-coating technique. The degradation performance of the composite photoanodes was evaluated in a PEC-coupled PMS (peroxymonosulfate) activation system using levofloxacin (LVF) as the target pollutant. The 2-CBVO photoanode achieved a degradation efficiency of 78.8 % for LVF (15 ppm) within 30 min, representing a 45.1 % improvement over the BiVO4 photoanode. The pseudo-first-order rate constant for the degradation of LVF was determined to be 4.43 × 10−1 min−1. Photoelectrochemical analysis confirmed that CuFeO2 loading and PMS introduction enhanced photogenerated carrier separation, promoting LVF degradation. Radical trapping experiments indicated that h+, OH, SO4− and O2− were the primary reactive species in the degradation process. Both theoretical calculations and experimental results confirmed that the internal electric field at the composite interface directs from BiVO4 to CuFeO2, facilitating electron transfer from CuFeO2 to BiVO4 and onward to the cathode surface via the external circuit. Cyclic stability tests demonstrated that the 2-CBVO composite photoanode retained 90.0 % of its activity after five cycles, indicating excellent stability and significant potential for water treatment applications.

Design and fabrication of double heterojunctions of WO3/BiVO4/Cu2O photoanode for photoelectrochemical water splitting

To overcome the shortcoming of photon-generated electrons and holes recombination for WO3 photoanode in photoelectrochemical (PEC) water splitting, WO3/BiVO4/Cu2O n-n-p double heterojunction photoanode was designed and prepared by a simple drop-casting method and electrodeposition, which can enhance the photoelectrochemical performance of the WO3 photoanode due to the successful constructions of the type II heterojunctions. The ternary photoanode increased the photocurrent density from 0.50 mA·cm−2 for WO3 photoanode at 1.23 V (vs. RHE) to 5.00 mA·cm−2 for WO3/BiVO4/Cu2O photoanode. Compared with WO3 photoanode, the visible light absorption range of the WO3/BiVO4/Cu2O photoanode is expanded (verified in the UV–vis absorption curve) and the utilization efficiency of visible light is significantly improved. The mechanism of PEC process is also discussed in detail, which is attributed to the fact that the carrier separation efficiency is greatly improved by the migration of photogenerated electrons and holes in opposite directions at the double heterojunctions interface.

Interfacial [S─Cu─C] Bonds Induced π-d Electron Coupling Toward Modulating Charge Transfer for Efficient Solar Water Oxidation.

Regulating the interfacial electric field to achieve rapid charge transfer is crucial for superior photoelectrochemical water splitting. Herein, the ultra-thin hydrogen-substituted graphdiyne (HsGDY) is precisely assembled on the surface of CdS nanorod array (Cu-CdS-HsGDY) by an in situ polymerization strategy. The strong π-d electron coupling is aroused by the delocalized π electrons of HsGDY and the delocalized d electrons of CdS through the interfacial [S─Cu─C] bonds. The strong interfacial electric field can effectively promote the charge localization distribution and reduce the charge transfer resistance. The optimized Cu-CdS-HsGDY photoanode obtain a photocurrent density as high as 4.83 mA cm-2 at 1.23 V versus reversible hydrogen electrode in neutral electrolyte solution under AM 1.5G illumination, which is 6.8 times that of the pristine CdS. Moreover, the photoanode maintains an initial photocurrent density of 84% within 4 h without any assistance of sacrificial agents, which is a rather competitive performance of similar sulfide photoanodes. The mechanism of strong π-d electron coupling on interfacial charge transfer and surface reaction kinetics is investigated by transient spectroscopy measurements, density functional theory calculation, and finite element simulation analysis. This work provides new insights into designing a reasonable interface structure to regulate charge transfer for achieve efficient PEC water splitting.

Interfacial Engineering‐Assisted Energy Level Modulation Enhances the Photoelectrochemical Water Oxidation Performance of Bismuth Vanadate Photoanodes

AbstractBiVO4 faces significant challenges for widespread application in photoelectrochemical (PEC) water oxidation due to its poor hole transport ability, high surface defect density, and sluggish water oxidation reaction kinetics. Employing interfacial engineering to assist in energy level modulation is an effective strategy to address these challenges. Herein, a CuCrO2 hole transport layer (HTL) is coupled and further grew NiCo‐MOF in situ to prepare a NiCo‐MOF‐CuCrO2‐BiVO4 composite photoanode. The novel composite photoanode not only achieves a photocurrent density of 5.75 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (vs RHE) but also maintains stable operation for over 24 h. Comprehensive physicochemical characterization and density‐functional theory calculations confirm that the built‐in electric field generated by the p–n heterojunction formed between the CuCrO2 HTL and BiVO4 photoanode enhances the hole transport ability. Moreover, the NiCo‐MOF chelated on the photoanode surface not only passivates the surface defect states but also accelerates the kinetics of the water oxidation reaction. Under the synergistic effect of dual modification, the PEC water oxidation performance of the BiVO4 photoanode is dramatically improved. This pioneering work presents a MOF/HTL/BiVO4 configuration that provides a blueprint for the future development of integrated photoanodes for efficient solar energy conversion.

What Limits the Stability Performance of Polymeric Carbon Nitride Photoanode for Photoelectrochemical Water Splitting?

Although many researches have been reported about the high performance of polymeric carbon nitride (PCN) photoanode, but it is still limited by poor stability. In this work, PCN nanosheets photoanode is used as a platform to investigate the sources of this issue. Through a combination of photoelectrochemical, X-ray Photoelectron Spectroscopy (XPS), and Potentiostatic Electrochemical Impedance Spectroscopy (PIES) measurements, it is shown that amounts of C═O bonds will form on the surface of PCN photoanodes, which limited the separation of the photogenerated carriers. To solve this problem, the TiO2 is deposited on PCN photoanode (named as PCN/TiO2) to improve the stability. And the PEC water splitting studies revealed that the stability of PCN/TiO2 photoanode is improved significantly as its photocurrent density can still maintain 90% after 3 h of reaction. This study provides a new way to understand the mechanism for the performance decrease of PCN photoanode and hope to inspire more powerful strategies to improve PCN photoanode stability.

Fe−N Co‐Doped BiVO4 Photoanode with Record Photocurrent for Water Oxidation

AbstractBismuth vanadate (BVO) ranks among the most promising photoanodes for photoelectrochemical (PEC) water splitting. Nonetheless, slow charge separation and transport, besides the sluggish water oxidation kinetics, are key barriers to its photoefficiency. Here, we present a co‐doping strategy that significantly improves the charge separation performance of BVO photoanodes. We found that, under standard one sun illumination, the Fe−N co‐doped BVO photoanode (Fe−N−BVO) by N‐coordinated Fe precursor reaches a record photocurrent density of 7.01 mA cm−2 at 1.23 V vs RHE after modified a surface co‐catalyst (FeNiOOH), and exhibits an outstanding stability. By contrast, much lower photocurrent density is obtained for the N‐doped, Fe‐doped and Fe/N‐doped BVO photoanode with separated N and Fe precursors. The detailed experimental characterizations show that the high activity of the Fe−N co‐doped BVO photoanode is attributed to the enhanced photo‐induced bulk charge separation, as well as the accelerated surface water oxidation kinetics. XPS, EXAFS and DFT calculations clearly show that, instead of formation of deep trapping state in the individually doped BVO, the co‐doping of Fe−N into BVO generates Fe‐based electronic states just below the bottom of conduction band and N‐derived states just above the top of valence band. Such modulations in electronic structure enable the efficient trap of the electrons and holes to enhance the separation of photo‐induced carriers, but hinder the charge recombination originated from the deep trapping sites.

Enhanced water splitting on (010) facet-exposed BiVO4 photoanode with improved carrier injection efficiency

Transition metal oxide semiconductors, noted for their stability and suitable bandgap, are promising photoanodes for water splitting. Surface engineering is critical to tackle issues like low carrier mobility and charge recombination, stemming from atomic arrangement and Fermi level differences. While exposing dominant crystal facets boosts photocatalytic capability, it can hinder carrier injection into the electrolyte. In this study, BiVO4 films with various facet exposures were synthesized and characterized using scanning electron microscopy and x-ray diffraction to confirm their morphology and crystalline structure. Mott–Schottky analysis was employed to investigate changes in the band structure near the semiconductor–electrolyte interface, revealing that high (010)-BiVO4 facet exposure enhances carrier separation but reduces injection efficiency. The results from photoconductive atomic force microscopy tests demonstrated that enhanced band bending at the semiconductor interface improves hole transfer. Coating the (010)-BiVO4 photoanode with MoS2 and an amorphous ZrO2 interlayer yielded a photocurrent density of 0.6 mA cm−2 at 1.2 V (vs RHE) under AM 1.5 G illumination, tripling the pristine photoanode's performance and nearly tripling water splitting efficiency. Mechanism revealing the improved photoelectrochemical performance is attributed to a greater band bending on the BiVO4 surface, enhancing hole injection dynamics. This work provides a feasible strategy for a deeper understanding of the intrinsic mechanisms of facet engineering and improving the activity of photoanodes.

Tailoring Hematite Photoanodes for Improved PEC Performance: The Role of Alcohol Species Revealed by SHAP Analysis.

We explore the synergistic effects of TiO2 underlayers and varied alcohol species in the precursor solutions on the photoelectrochemical (PEC) performance of hematite photoanodes. Utilizing a robust machine learning (ML) framework combined with comprehensive analytical data sets, we systematically investigate how these modifications influence key physical and chemical properties, directly impacting the efficiency of water splitting processes. Our approach employs an ML model that integrates SHapley Additive exPlanations (SHAP) to quantitatively assess the impact of each dominant descriptor selected in the analytical data on the PEC performance, and they were combined with the SHAP values' dependence on the experimental operations. Specifically, we focus on the type of alcohol (methanol, ethanol, butanol, and 2-ethyl-1-butanol) used in the precursor solutions as the experimental operation, examining their effects on the dominant descriptors selected in the analytical data. The results from the SHAP analysis reveal that different alcohol species significantly alter the physicochemical properties at the hematite/TiO2 interface and in bulk hematite. These changes are primarily manifested in the modulation of the density of states and resistance to promote the charge carrier transport. For example, ethanol and butanol were found to enhance the electron density of states at the interface, which correlates with higher photocurrent outputs and improved PEC activity. In contrast, methanol showed a less pronounced effect, suggesting a nuanced interaction between the alcohol molecular structure and hematite surface chemistry. These findings not only underscore the importance of tailored precursor solution chemistry for enhancing PEC performance but also highlight the power of ML tools in uncovering the underlying physical and chemical mechanisms that govern the behavior of complex material systems. This study sets a foundational approach where ML can bridge the gap between empirical observations and theoretical understanding, leading to the rational design of energy materials.

Interfacial binding-enhanced charge transport for CoFe-MOF/Fe2O3 photoanodes with excellent PEC performance

Interfacial charge-transfer efficiency determines the photoelectrochemical (PEC) performance of Fe2O3-based heterojunction photoanodes. Herein, we present Fe2O3 nanoarrays coated by CoFe bimetal organic framework (CoFe-MOF) nanolayers (CoFe-MOF/F) via in-situ solvothermal method. The resulting CoFe-MOF/F photoanode has a current density of 2.2 mA cm−2 at 1.23 V vs. RHE, which is about 2.2 times that of pristine Fe2O3. Moreover, the CoFe-MOF/F photoanode shows a negative shift of onset potential, and excellent long-term PEC stability. The in-situ synthesized CoFe-MOF on the photoanode surface enhances the interaction force between the photoanode and the photoanode and strengthen the interface binding, therefore, the interface defects are reduced and the transfer efficiency of interfacial carriers increases, wich effectively improve the performance of the photoanode. This work provides an in-situ strategy for enhancing the binding force between the cocatalyst and the photoanode to improve the PEC performance of the photoelectrode. This approach is not only effective but also scalable, offering the prospect of optimizing the performance of a wide range of photoanode materials.