Photoelectrochemical Hydrogen Production Research Articles

Novel synthesis of Ti–Fe2O3/MIL-53(Fe) via the in situ process for efficient photoelectrochemical water oxidation

The slow kinetics of water oxidation has become a challenge for photoelectrochemical hydrogen production. Here, a novel organic-inorganic integrated photoanode system was constructed by using MIL-53(Fe) formed during the in-situ etching process as a cocatalyst to modify Ti–Fe2O3. The photocurrent density of Ti–Fe2O3/MIL-53(Fe) reaches 2.5 mA/cm2, 10 times that of bare Ti–Fe2O3 at 1.23 V vs. RHE, and the water oxidation photocurrent onset potential shifts 105 mV negatively. Ti–Fe2O3/MIL-53(Fe) reaches 52% at 390 nm for IPCE. The excellent photoelectrochemical performance is due to iron oxide clusters boost charge separation and transfer, in-situ etching exposes more reactive sites, and the tight connection reduces interfacial resistance, which greatly accelerates the surface kinetics of Ti–Fe2O3. The in-depth understanding is provided for in-situ modification of photoanodes by metal organic frameworks in this work.

Thermal Effect on Photoelectrochemical Water Splitting Toward Highly Solar to Hydrogen Efficiency.

Photoelectrochemical (PEC) hydrogen production is an emerging technology that uses renewable solar light aimed to establish a sustainable carbon-neutral society. The barriers to commercialization are low efficiency and high cost. To date, researchers have focused on materials and systems. However, recent studies have been conducted to utilize thermal effects in PEC hydrogen production. This Review provides a fresh perspective to utilize the thermal effects for PEC performance enhancement while delineating the underlying principles and equations associated with efficiency. The fundamentals of the thermal effect on the PEC system are summarized from various perspectives: kinetics, thermodynamics, and empirical equations. Based on this, materials are classified as plasmonic metals, quantum dot-based semiconductors, and photothermal organic materials, which have an inherent response to photothermal irradiation. Finally, the economic viability and challenges of these strategies for PEC are explained, which can pave the way for the future progress in the field.

Remarkable improvement of photoelectrochemical water splitting in pristine and black anodic TiO2 nanotubes by enhancing microstructural ordering and uniformity

Efficient photoelectrochemical (PEC) water splitting is crucial for future energy and sustainable world. We here report on the improvement of PEC activity of anodic TiO 2 nanotubes (TNTs) by enhancing tube ordering and subsequent electrochemical reduction. TNTs were prepared by two-step anodic oxidisation from an organic electrolyte containing fluoride ions. The effects of first-step anodisation time on the ordering of TNTs and subsequent electrolytic reduction were investigated on the PEC performance under simulated solar light spectrum. The photocurrent densities of TNTs anodised for 1 h, 4 h and subsequently reduced are about 25.12 μA cm −2 , 51.76 μA cm −2 and 126.89 μA cm −2 , respectively, at 1.23 V vs RHE and their conversion efficiency of light to electrical energy achieved are about 0.016%, 0.04% and 0.08% respectively. Electrochemical impedance spectroscopy (ESI) curves revealed the improved PEC water splitting confirmed by sharper charge carrier separation and enhanced charge transfer in highly ordered pristine and black TNTs. This improvement of PEC in dopant-free TNT is at the first instance interpreted by enhancing TNT ordering and uniformity achieved by prolonging of the first-step anodisation time and its effect on the electronic band structure of TNTs. This significant effect on PEC performance of pristine TNT under visible light absorption takes place due to the induced surface defects and slower recombination rates of hole and electron. This demonstrates an efficient economic materials production appraoch for PEC hydrogen production. • High efficient PEC water splitting using pristine and black nanotubes (TNTs). • The photocurrent density of black TNT is about 126.89 μA cm −2 at 1.23 V vs RHE. • The amount of generated H 2 was estimated about 57.96 cm 3 during 1 h. • Microstructural ordering of TNTs enhanced the PEC water splitting.

Role of active area on photoelectrochemical water-splitting performance of inverse opal CuBi2O4 photocathodes

Copper bismuth oxide(CuBi2O4), a ternary metal oxide is considered as one of the best photocathodes for photoelectrochemical water splitting. However, to date, the majority of research activities have been aimed at developing photocathodes at laboratory scale (≤1 cm2 electrochemical active area) and the issues that arise with scaling up have scarcely been addressed. Herein, we demonstrate a layered self-assembly method for fabricating uniform anddifferent electrochemical active area (1–15 cm2) inverse opal structured CuBi2O4 photocathodes, intending to validate it for photoelectrochemical hydrogen evolution under solar irradiation. After scaling up, it was found that CuBi2O4 with an active area of 5 cm2 exhibits the best photocurrent density (3.24 mA/cm2 at 0.6 V vs. RHE) and Faradaic efficiency (98.06 %). The scaling-up strategy and low-cost method employed for the fabrication of photocathodes could be expanded to large-scale applications associated with the manufacturing of highly efficient photoelectrochemical hydrogen production devices.

Design of novel metal chalcogenide photoanodes supported with reduced graphene oxide for improvement of photoelectrochemical hydrogen evolution

Designing new photoanodeswith high efficiency provides an effective route to develop photoelectrochemical hydrogen production.In this work, quaternary metal chalcogenides (CdZnMSSe (M: Ni, Cu, Mo)) and reduced graphene oxide- quaternary metal chalcogenide (RGO-CdZnMSSe) composite films are fabricated by simple one-step electrodeposition process. The photoanodes formed of quaternary metal chalcogenides and the incorporation of RGO in these composite films increase charge transfer capability and separation ability compared to cadmium-based photoanodes, leading to enhancement of the photoelectrochemical hydrogen production activity. A superior photocurrent response is recorded for RGO(0.25)-Cd0.8Zn0.2Ni0.2S0.2Se0.8 (5.34 mA cm−2 at 0.8 V vs RHE). In addition, the maximum ABPE value of RGO(0.25)-Cd0.8Zn0.2Ni0.2S0.2Se0.8 is determined as 1.95%. The achieved results offer a new insight into highly efficient next generation-photoanodes to convert solar energy to hydrogen.

Boosting photoelectrochemical chlorine and hydrogen production with oxygen vacancy rich TiO2 photoanodes

Photoelectrochemical chlorine (Cl2) evolution as the anodic reaction of solar hydrogen production is helpful for increasing the additional value of hydrogen and reducing production cost. In this work, chemically stable TiO2 nanotubes are used as the photoanodes for photoelectrochemical chlorine and hydrogen production. Oxygen vacancies (VO) are introduced by post-annealing in H2/N2 atmosphere. By controlling the post-annealing temperature, concentration of oxygen vacancies is tuned efficiently. Systematic photoelectrochemical measurements reveal that the oxygen vacancies significantly enhance the PEC performance for Cl2 production with respect to the pristine TiO2. The sample post-annealed at 450 °C in H2/N2 achieves the highest Cl2 production rate of 37.12 μmol h−1 cm−2 with a Faradaic efficiency of 73.2% that resulted in fast degradation of methyl orange at a speed of 5.73 mg h−1 cm−2. Furthermore, photocurrent of the two-electrode cell constructed with the VO-rich TiO2 is strongly increased by 250%, demonstrating that introducing oxygen vacancies is a promising way for promoting the photoelectrochemical performance for Cl2 and H2 production. By careful measuring the Faradaic efficiency of various photoanodes, it is revealed that the strongly boosted up Cl2 production is owing to enhancing utilization of photogenerated holes via the oxygen vacancies.

PbS Quantum Dots-Decorated BiVO4 Photoanodes for Highly Efficient Photoelectrochemical Hydrogen Production.

While metal oxides such as TiO2, Fe2O3, WO3, and BiVO4 have been previously studied for their potential as photoanodes in photoelectrochemical (PEC) hydrogen production, their relatively wide band-gap limits their photocurrent, making them unsuitable for the efficient utilization of incident visible light. To overcome this limitation, we propose a new approach for highly efficient PEC hydrogen production based on a novel photoanode composed of BiVO4/PbS quantum dots (QDs). Crystallized monoclinic BiVO4 films were prepared via a typical electrodeposition process, followed by the deposition of PbS QDs using a successive ionic layer adsorption and reaction (SILAR) method to form a p-n heterojunction. This is the first time that narrow band-gap QDs were applied to sensitize a BiVO4 photoelectrode. The PbS QDs were uniformly coated on the surface of nanoporous BiVO4, and their optical band-gap was reduced by increasing the number of SILAR cycles. However, this did not affect the crystal structure and optical properties of the BiVO4. By decorating the surface of BiVO4 with PbS QDs, the photocurrent was increased from 2.92 to 4.88 mA/cm2 (at 1.23 VRHE) for PEC hydrogen production, resulting from the enhanced light-harvesting capability arising from the narrow band-gap of the PbS QDs. Moreover, the introduction of a ZnS overlayer on the BiVO4/PbS QDs further improved the photocurrent to 5.19 mA/cm2, attributed to the reduction in interfacial charge recombination.

Bandgap Reduction and Enhanced Photoelectrochemical Water Electrolysis of Sulfur-doped CuBi2O4 Photocathode

As interest in hydrogen energy grows, eco-friendly methods of producing hydrogen are being explored. CuBi2O4 is one of the p-type semiconductor cathode materials that can be used for photoelectrochemical hydrogen production via environment-friendly water electrolysis. CuBi2O4 has a bandgap of 1.5 – 1.8 eV which allows it to photogenerate electrons and holes from the absorption of visible light. This study investigated the effect of sulfur doping on the bandgap and photoelectrochemical water reduction properties of CuBi2O4. Sulfur-doped CuBi2O4 thin films were electrochemically synthesized using a nitrate-based precursor solution with thiourea. This was followed by two-step annealing in an Ar atmosphere, which effectively prevented the oxidation of sulfur. Sulfur doping up to 0.1 at% led to the expansion of the lattice volume of the CuBi2O4. The bandgap was reduced from 1.9 eV to 1.5 eV with increasing doping concentration, which resulted in the enhancement of photoelectrochemical current density by ~240%. X-ray photoelectron spectroscopy showed that sulfur-doping reduced oxygen vacancies with increasing doping concentration, confirming that the enhanced photoelectrochemical properties resulted from the reduction in bandgap, not from any extrinsic factor such as oxygen vacancies. Further studies of sulfur-doped CuBi2O4 to improve surface coverage are expected to lead to a more promising photoelectrochemical cathode material.

Facile synthesis of flexible and scalable Cu/Cu2O/CuO nanoleaves photoelectrodes with oxidation-induced self-initiated charge-transporting platform for photoelectrochemical water splitting enhancement

Photoelectrochemical hydrogen production is considered a promising candidate for artificial photosynthesis. Herein, a facile oxidation method is proposed for fabricating flexible and scalable Cu/Cu2O/CuO nanoleaves photoelectrodes. The process creates a thin Cu2O layer at the oxygen-lacking interface between Cu and CuO ingredients and can act as a self-initiated charge-transporting platform in photoelectrochemical water splitting. The proposed Cu/Cu2O/CuO nanoleaves have been demonstrated as a promising photoelectrode material superior to that of similar photoelectrodes fabricated by other methods. Despite the impressive performance, the Cu/Cu2O/CuO photoelectrodes are subjected to annealed at different temperatures and, the Cu/Cu2O/CuO photoelectrode annealed at 100 °C displays a remarkable hydrogen evolution of 4.76 μmol/hcm2, in comparison. A possible mechanism for such improvements is suggested based on the self-initiated Cu2O layer and surface reconstruction with post-annealing. Namely, the charge transport layer prevents photocorrosion by improving the photostability and reducing the grain boundaries by increasing the size of the particles, thereby enhancing efficiency via fast charge carrier transfer. Accordingly, our exploration introduces the self-initiated charge-transporting platform and flexible photoelectrodes for the improvement of photoelectrochemical hydrogen production based on the Cu/Cu2O/CuO nanoleaves.

Cover Feature: Quantum Dots, Passivation Layer and Cocatalysts for Enhanced Photoelectrochemical Hydrogen Production (ChemSusChem 3/2023)

The Cover Feature shows the strategies to improve the photoelectrochemical hydrogen evolution of quantum dot (QD)-based semiconductors (yellow balls) by applying a co-catalyst (buried grey balls) or a passivation layer (blue layers) as shown in the left electrode. The co-catalyst facilitates the charge-transfer kinetics by providing active sites for reactive species, and the passivation layer helps to protect QDs from oxidation as well as provide more conductive pathways for electrons. More information can be found in the Review by H. Kim, A. Choe, S. B. Ha and co-workers.

Enhanced photoelectrochemical hydrogen production by a composite photoanode constructed with TiO2 nanorods and Cu-modified NH2-MIL-125

It is of great interest to enhance the photoelectrochemical hydrogen production rate of TiO2 by utilizing the new Metal-organic frameworks material such as NH2-MIL-125(Ti), but the assembly method and its details often bring about a significant difference in performances of the composite photoelectrode. In this study, NH2-MIL-125 is grown on the surface of TiO2 nanorods by an in-situ strategy, and then Cu-modified NH2-MIL-125/TiO2 photoanode is prepared by impregnation method. Based on the characterization of SEM, UV-VIS DRS and PL spectra, the disc-like NH2-MIL-125 can improve the light absorptance in visible light region, and the modification of Cu+/Cu2+ can inhibit the charge recombination in NH2-MIL-125/TiO2 photoanode, resulting in the improved the carrier transport ability verified by EIS and IMPS. Under AM 1.5 illumination, H2 evolution rate over Cu-NH2-MIL-125/TiO2 is boosted a great extent, which is 4.6 times than that of pristine TiO2.

One-step construction of buried a-Si/c-Si junction photocathodes for boosting photoelectrochemical hydrogen production

The activity of Si-based photocathode for photoelectrochemical hydrogen production is mainly restricted by inadequate photovoltage and easy (photo)-corrosion, requiring complex doping or deposition techniques for improvement. Herein, a mild and feasible strategy is proposed to fabricate an amorphous Si/crystal Si (a-Si/c-Si) junction photocathode with co-deposited Pt cocatalyst. The a-Si layer acts as an electron transfer mediator to form an a-Si/c-Si buried junction with large energy band shift, thereby ensuring facile charge transfer. Meanwhile, the a-Si layer serves as a growth substrate to obtain controllable Pt nanoparticles. The Pt/a-Si/c-Si photocathode shows an onset potential of 0.42 V vs reversible hydrogen electrode (VRHE). A photocurrent up to − 35.0 mA cm−2 at 0 VRHE is obtained on Pt/a-Si/c-Si, which is much higher than that without a-Si layer. This study provides a practical manner for improving the photoresponse of planar Si-based photocathodes based on the construction of Si junction.

Effect of reaction temperature on morphology and photoelectrochemical performance of titanium dioxide

• Nanorod and nanowire mixed-phase of TiO 2 is synthesized via hydrothermal method. • Effect of reaction temperature on photoelectrochemical performance is investigated. • A superior photoelectrochemical water splitting performance was obtained. Titanium dioxide (TiO 2 ) is best photoanode for photoelectrochemical water splitting. Here, the effect of reaction temperature on titanium dioxide nanorods is studied via a hydrothermal synthesis method. The results reveal the reaction temperature has high impact on morphology, bandgap and photoelectrochemical properties. The photoelectrochemical performance of TiO 2 is enhanced as reaction temperature increase. When reaction temperature increases from 130℃ to 180℃, the photocurrent density and hydrogen generation increase from 0.65 mA/cm 2 , 72.49 μmol/cm 2 to 1.84 mA/cm 2 , 126.86 μmol/cm 2 respectively These results suggest the potential for the synthesis and usage of transition metal oxides/sulfides for efficient photoelectrochemical hydrogen production.

Quantum Dots, Passivation Layer and Cocatalysts for Enhanced Photoelectrochemical Hydrogen Production.

Solar-driven photoelectrochemical (PEC) hydrogen production is one potential pathway to establish a carbon-neutral society. Nowadays, quantum dots (QDs)-sensitized semiconductors have emerged as promising materials for PEC hydrogen production due to their tunable bandgap by size or morphology control, displaying excellent optical and electrical properties. Nevertheless, they still suffer from anodic corrosion during long-term cycling, offering poor stability. This Review discussed advancements to improve long-term stability of QDs particularly in terms of cocatalysts and passivation layers. The working principle of PEC cells was reviewed, along with all important configurations adopted over recent years. The equations to assess PEC performance were also described. A greater emphasized was placed on QDs and incorporation of cocatalysts or passivation layers that could enhance the PEC performance by influencing the charge transfer and surface recombination processes.

Unravelling the Interfacial Dynamics of Bandgap Funneling in Bismuth-Based Halide Perovskites.

An environmentally friendly mixed-halide perovskite MA3 Bi2 Cl9- x Ix with a bandgap funnel structure has been developed. However, the dynamic interfacial interactions of bandgap funneling in MA3 Bi2 Cl9- x Ix perovskites in the photoelectrochemical (PEC) system remain ambiguous. In light of this, single- and mixed-halide lead-free bismuth-based hybrid perovskites-MA3 Bi2 Cl9- y Iy and MA3 Bi2 I9 (named MBCl-I and MBI)-in the presence and absence of the bandgap funnel structure, respectively, are prepared. Using temperature-dependent transient photoluminescence and electrochemical voltammetric techniques, the photophysical and (photo)electrochemical phenomena of solid-solid and solid-liquid interfaces for MBCl-I and MBI halide perovskites are therefore confirmed. Concerning the mixed-halide hybrid perovskites MBCl-I with a bandgap funnel structure, stronger electronic coupling arising from an enhanced overlap of electronic wavefunctions results in more efficient exciton transport. Besides, MBCl-I's effective diffusion coefficient and electron-transfer rate demonstrate efficient heterogeneous charge transfer at the solid-liquid interface, generating improved photoelectrochemical hydrogen production. Consequently, this combination of photophysical and electrochemical techniques opens up an avenue to explore the intrinsic and interfacial properties of semiconductor materials for elucidating the correlation between material characterization and device performance.

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Osmotic-Enhanced-Photoelectrochemical Hydrogen Production Based on Nanofluidics

Photoelectrochemical hydrogen evolution from biomass conversion using perovskite solar cells

Lignocellulosic biomass presents a renewable alternative to fossil carbon sources for the production of commodity chemicals and fuels. Photoelectrochemical biomass conversion produces carbon-free fuel in the form of molecular hydrogen and simultaneously provides a source of value-added chemical products. Recently in Nature Communication , S.Y. Jang, J.-W. Jang, J. Ryu, and co-workers reported bias-free photoelectrochemical solar hydrogen production coupled to lignocellulosic biomass degradation using a perovskite-based photocathode with anodic lignin depolymerization mediated by phosphomolybdic acid. Lignocellulosic biomass presents a renewable alternative to fossil carbon sources for the production of commodity chemicals and fuels. Photoelectrochemical biomass conversion produces carbon-free fuel in the form of molecular hydrogen and simultaneously provides a source of value-added chemical products. Recently in Nature Communication , S.Y. Jang, J.-W. Jang, J. Ryu, and co-workers reported bias-free photoelectrochemical solar hydrogen production coupled to lignocellulosic biomass degradation using a perovskite-based photocathode with anodic lignin depolymerization mediated by phosphomolybdic acid.

Defect-rich MoS2/NiS2 nanosheets loaded on SiNWs for efficient and stable photoelectrochemical hydrogen production

Photoelectrochemical (PEC) reaction with efficient, stable, and cost-effective photocathodes using non-precious metals will be one of the most environmentally friendly technologies for hydrogen (H2) generation under the worldwide pressure for carbon neutrality. Herein, a new 3-dimentional (3D) SiNWs@MoS2/NiS2 photocathode was designed and synthesized. Defect-rich MoS2/NiS2 nanosheets on silicon nanowires (SiNWs) provide more active sites to promote charge transfer and photo-generated electron-hole separation. Meanwhile, the 3D structure of the photocathode provides an effective charge transfer mode and an open channel for rapid H2 release. The SiNWs@MoS2/NiS2 photocathode exhibits the maximum photocurrent density (21.4 mA·cm−2 at 0.9 V vs. RHE), highest H2 production rate (183 μmol·h−1), smallest diffusion resistance (34.7 Ω), and excellent catalytic stability for more than 10 h at pH = 7. Based on density function theory calculation, the MoS2/NiS2 nanosheets are conducive to chemical adsorption of H2 intermediates, which are crucial for the maintenance of the composite photocathode in PEC H2 production.

Remarkable photoelectrochemical activity of titanium dioxide nanorod arrays sensitized with transition metal sulfide nanoparticles for solar hydrogen production

The synthesis of a cost-effective and efficient catalyst is vital for accelerating the rate of photoelectrochemical hydrogen production. Here, titanium dioxide nanorods sensitized by nickel sulfide, cadmium sulfide, and zinc sulfide nanoparticles (ZnS/CdS/NiS@TiO2) were developed as a photoanode material via a hydrothermal process followed by the successive ionic layer adsorption and reaction. The morphological analysis of ZnS/CdS/NiS@TiO2 revealed the nanorods (TiO2) phase in which NiS, CdS, and ZnS nanoparticles are distributed homogeneously. The photoelectrochemical performance analysis of ZnS/CdS/NiS@TiO2 furnished a maximum photocurrent density of 6.1 mA/cm2, which is 7.6 times higher than that of pure TiO2 (0.8 mA/cm2). Additionally, the sensitized TiO2 nanorod arrays as a photoanode show high photoelectrochemical hydrogen production of 491.52 μmol/cm2, which is 4.9 times higher than that of pristine TiO2 (99.61 μmol/cm2) over 6 h under simulated solar irradiation. These results suggested the potential for the synthesis and usage of novel hybrids of TiO2 nanorods decorated with transition metal chalcogenides for efficient photoelectrochemical hydrogen production.

A Room Temperature Electrodeposition Method to Develop High Performance Metal-Chalcogenide Nanowire Array-Based Photoelectrochemical (PEC) Device for Solar Hydrogen Production

Photoelectrochemical (PEC) water splitting has emerged as a significant and promising technique for the generation of low-cost, highly efficient, and sustainable hydrogen(H2) fuel. Currently, PEC hydrogen production has been successfully demonstrated on a laboratory scale. However, the commercial viability of PECs depends critically on the cost of H2 produced by the PECs, which is affected by the cost of PEC construction. Here we consider electrodeposition as a promising method to fabricate multijunction PEC cells because this is an inexpensive solvent-based technique operated at low temperature with the ability to control the film thickness by varying the deposition potential and charge passed which can be optimized to perform like other matured and expensive vapor-based deposition techniques functioning at high temperatures.In this research work, we report a room temperature, low-cost electrodeposition method to synthesize metal chalcogenide semiconductor thin films and nanowire arrays in superstrate configuration and demonstrate its applicability for solar hydrogen production. Specifically, the talk will address the effect of electrodeposition parameters and post-treatment on observed photocurrent and photovoltage responses. By optimizing the deposition potential and deposition charge we were able to achieve photocurrent densities exceeding 15 mA cm-2 for thin films and nanowire arrays when tested using regenerative redox couples.Finally, the talk will cover the aspects of developing a buried junction PV/PEC using electrodeposited chalcogenide semiconductors for solar hydrogen production.