Photoelectrocatalytic Hydrogen Production Research Articles

Photoelectrocatalytic hydrogen production: Hydrogen production principle, performance optimization strategy, application and prospect

Photoelectrocatalytic hydrogen production: Hydrogen production principle, performance optimization strategy, application and prospect

Progress in Promising Semiconductor Materials for Efficient Photoelectrocatalytic Hydrogen Production.

Photoelectrocatalytic (PEC) water decomposition provides a promising method for converting solar energy into green hydrogen energy. Indeed, significant advances and improvements have been made in various fundamental aspects for cutting-edge applications, such as water splitting and hydrogen production. However, the fairly low PEC efficiency of water decomposition by a semiconductor photoelectrode and photocorrosion seriously restrict the practical application of photoelectrochemistry. In this review, the mechanisms of PEC water decomposition are first introduced to provide a solid understanding of the PEC process and ensure that this review is accessible to a wide range of readers. Afterwards, notable achievements to date are outlined, and unique approaches involving promising semiconductor materials for efficient PEC hydrogen production, including metal oxide, sulfide, and graphite-phase carbon nitride, are described. Finally, four strategies which can effectively improve the hydrogen production rate-morphological control, doping, heterojunction, and surface modification-are discussed.

Testing the photo-electrocatalytic hydrogen production of polypyrrole quantum dot by combining with graphene oxide sheets on glass slide

Testing the photo-electrocatalytic hydrogen production of polypyrrole quantum dot by combining with graphene oxide sheets on glass slide

Cobalt-doped CsPbBr3 perovskite quantum dots for photoelectrocatalytic hydrogen production via efficient charge transport

Photoelectrochemical cells (PECs) based on all-inorganic perovskite quantum dots (QDs) have great potential for the catalytic splitting of water using sunlight due to their good photovoltaic properties and inexpensive manufacturing process. However, their development is severely constrained by their own large carrier transport barriers and poor water stability. Herein, we report the synthesis of cobalt doped CsPbBr3 perovskite quantum dots (Co-doped CsPbBr3 QDs) by hot-injection method and their preparation into FTO/c-TiO2/m-TiO2/Co-CsPbBr3 QDs photoanode devices, and further encapsulation of the devices using low-temperature conductive carbon paste (LTCC). The partial replacement of Pb2+ sites by Co2+ in Co-doped CsPbBr3 QDs with appropriate concentrations enhances the binding energy of QDs, forms impurity energy levels, reduces carrier transport barriers, improves carrier lifetime and carrier separation and transport rate, so as to improve optoelectronics purpose of catalytic activity. Ultimately, the Co-CsPbBr3 QDs photoanode produced 1.944 mA cm−2 at 1.23 VRHE under simulated sunlight (AM 1.5, 100 mW cm−2) and achieved a stable photocurrent density of more than 1 mA cm−2 for up to 5500 s in aqueous KOH solution. The development of effective all-inorganic perovskite quantum dots sheds light on the realization of catalysts for PEC water splitting.

Electrodeposition of Copper Oxides as Cost-Effective Heterojunction Photoelectrode Materials for Solar Water Splitting

Photoelectrocatalytic hydrogen production is crucial to reducing greenhouse gas emissions for carbon neutrality and meeting energy demands. Pivotal advances in photoelectrochemical (PEC) water splitting have been achieved by increasing solar light absorption. P-type Cu-based metal oxide materials have a wide range of energy band gaps and outstanding band edges for PEC water splitting. In this study, we first prepared Cu2O thin films using electrodeposition and fabricated a heterojunction structure of CuO/Cu2O by controlling annealing temperatures. The surface morphological, optical, and electrochemical properties were characterized using various analytical tools. X-ray and Raman spectroscopic approaches were used to verify the heterojunction of CuO/Cu2O, while surface analyses revealed surface roughness changes in thin films as the annealing temperatures increased. Electrochemical impedance spectroscopic measurements in conjunction with the Mott–Schottky analysis confirm that the CuO/Cu2O heterojunction thin film can boost photocurrent generation (1.03 mA/cm2 at 0 V vs. RHE) via enhanced light absorption, a higher carrier density, and a higher flat band potential than CuO and Cu2O thin films (0.92 and 0.08 mA/cm2, respectively).

The charge transfer pathway of g-C3N4 decorated Au/Ni3(VO4)2 composites for highly efficient photocatalytic hydrogen evolution

The photocharge carrier separation and migration within the heterostructure interface plays a pivotal role in the photoelectrocatalytic hydrogen production and the photocatalytic degradation activity. Herein, a series of the 2D/3D g-C3N4/Ni3(VO4)2 photocatalyst were successfully fabricated via a facile hydrothermal method. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet‐visible (UV‐vis), Brunauer‐Emmett‐Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The highest photocatalytic hydrogen production rate of g-C3N4/Au/Ni3(VO4)2 was about 3345 μmol g−1 h−1, which largely beyond that obtained of g-C3N4/Ni3(VO4)2 (501 μmol g−1 h−1), and pristine g-C3N4 (14 μmol g−1 h−1). The optimal apparent quantum efficiency was counted to be 6.8 % at λ = 420 nm and 1.1 % at λ = 600 nm. Moreover, the photocatalytic property of g-C3N4/Au/Ni3(VO4)2 could remain unchanged almost with 50 h in 5 cycles. The improvement of photocatalytic H2 yield is attributed to the result of rapid separation of photogenic carriers in space and surface plasmon resonance effect of Au nanoparticles.

Snowflake-Like Cu2S/MoS2/Pt heterostructure with near infrared photothermal-enhanced electrocatalytic and photoelectrocatalytic hydrogen production

Snowflake-like Cu2S/MoS2 heterostructures with varied compositions were constructed via a two-step hydrothermal method. The 45-Cu2S/MoS2 with 45 wt% Cu2S was found as the optimum catalyst, which displayed photothermal enhanced hydrogen evolution reaction (HER) performance under near infrared (NIR) irradiation. After electrochemical deposition of a tiny amount of Pt (45-Cu2S/MoS2/Pt-100s), Schottky barrier was formed between Pt nanoparticles and MoS2 nanosheets. Using 45-Cu2S/MoS2/Pt-100s as an electrocatalyst, low overpotential of 78 mV (@10 mV cm−2) and Tafel slope of 48 mV dec−1 were achieved with the assistance of NIR irradiation. The photoelectrochemical (PEC) hydrogen production performance of 45-Cu2S/MoS2/Pt-100s was also investigated. The optimal conversion efficiency of 45-Cu2S/MoS2/Pt-100s could reach 0.78% at 0.57 V (vs. reversible hydrogen electrode (RHE)). The control of the internal geometric and electronic structure of the catalysts and the aid of photothermal effect in this work provide new ideas for designing high-efficiency hydrogen evolution catalysts.

Uplifting the charge carrier separation and migration in Co-doped CuBi2O4/TiO2 p-n heterojunction photocathode for enhanced photoelectrocatalytic water splitting

Here, cobalt-doped copper bismuth oxide (Co-CuBi2O4) was synthesized via a facile hydrothermal method for photoelectrocatalytic (PEC) hydrogen production. The results disclosed that the 5% Co-doped CuBi2O4 has better PEC activity which is ∼3 fold higher than pristine CuBi2O4. The doping of cobalt in CuBi2O4 improves the interfacial charge transfer at an electrode/electrolyte interface and reduces the recombination rate of photogenerated electron-hole pairs. This higher performed 5% Co-doped CuBi2O4 photocathode further modified with TiO2-P25 to form a Co-CuBi2O4/TiO2 p‐n heterojunction. This Co-CuBi2O4/TiO2 photocathode displayed a photocurrent density of 330 μA cm−2 at +0.5 V vs. RHE which was ∼2 fold higher than Co-CuBi2O4. Because this p-n junction affords inner electric field in the space charge region that helps for further minimization of electron-hole recombination, which facilitate efficient charge separation and transport thereby enhance the PEC water reduction.

Enhanced photoelectrocatalytic hydrogen production performance of porous MoS2/PPy/ZnO film under visible light irradiation

Photoelectrochemical (PEC) water splitting provides a “green” approach for hydrogen production. However, the design and fabrication of high-efficient catalysts are the bottleneck for PEC water splitting owing to the involved thermodynamic and kinetic challenges. Herein, we report a new strategy for constructing a porous MoS2/PPy/ZnO thin film photocatalyst with large specific surface area and excellent conductivity to achieve photoelectrochemical water splitting under visible light irradiation. Porous PPy/ZnO was synthesized via template-assisted electrodeposition, and MoS2 was further electrodeposited to construct porous MoS2/PPy/ZnO thin film photocatalyst. The hydrogen evolution rate of MoS2/PPy/ZnO exhibits about 3.5-fold increase to 40.22 μmol cm−2 h−1 under visible light irradiation. The enhancement for photoelectrochemical hydrogen production is not only ascribed to enlarged specific surface area of the porous structure, but also attributed to the synergistic effects of MoS2 and porous PPy/ZnO, which could dramatically improve its visible light absorption capacity and enhance the separation and transfer of photogenerated charges. Thus, more abundant photogenerated electrons and holes participate in photoelectrochemical process, which significantly enhances its photoelectrochemical hydrogen production performance.

A comparative study of CuO deposition methods on titania nanotube arrays for photoelectrocatalytic ammonia degradation and hydrogen production

In this study, the deposition of CuO nanoparticles into titania nanotube arrays (TiNTAs) was prepared via two methods, i.e an in-situ anodization (AND) and a successive ionic layer adsorption reaction (SILAR). The two methods were compared in terms of their properties as efficient photoanodes in photoelectrocatalytic processes. FESEM and TEM imaging showed that the nanotubular structure was successfully generated. The bandgap energy was probed by UV-DRS analysis, revealing that CuO-TiNTAs SILAR had a lower bandgap than other samples. The photoelectrochemical responses of CuO-TiNTAs SILAR exhibit better activity compared to its counterpart. The maximum ammonia removal was achieved at 50.1% while as high as 235.7 μmol of hydrogen was generated over 120 min under Hg lamp illumination, by the use of CuO-TiNTAs SILAR. We thereby conclude that, for the given experimental conditions, CuO-TiNTAs SILAR is a better photoanode than CuO-TiNTAs AND concurrently eliminate ammonia and produce hydrogen in a photoelectrochemical setup.

Promoting the photo-induced charge separation and photoelectrocatalytic hydrogen generation: Z-scheme configuration of WO3 quantum nanodots-decorated immobilized Ti/TiO2 nanorods

The photoelectrocatalytic hydrogen production, especially using 1D TiO2 nanostructures, has been considered as a clean and sustainable approach to cope with energy crisis. Nevertheless, the large band gap energy of TiO2 and the rapid photo-induced charges recombination have limited its practical application. Therefore, in this study, WO3 quantum nanodots were employed with immobilized TiO2 nanorod arrays (TNRs-WQNDs) to tackle these drawbacks. Based on the results, the incorporation of WQNDs ameliorated both the optical and photoelectrochemical properties of TNRs. In this relation, the introduction of WQNDs into TNRs lattice using 10 mg WCL4 (TNRs-WQNDs (10)), as the optimum amount of tungsten precursor, not only made band gap energy much narrower (from 3 to 2.1 eV), but also significantly improved the photocurrent density from 0.92 to 1.67 mA/cm2 (at 1.23 V vs. RHE). In addition, both the STH and photoconversion efficiencies of TNRs-WQNDs (10) were about 1.7 and 1.5 times more than those of pure TNRs, respectively. As a result of these enchantments, the coupling of WQNDs with TNRs was able to increase the photoelectrocatalytic hydrogen production from 1.4 to 2.4 mmol under UV irradiation. An acceptable photoelectrocatalytic performance was further observed under visible light irradiation, where TNRs-WQNDs (10) could generate almost 1.5 mmol of hydrogen. Meanwhile, by investigating the mechanism of photoelectrocatalytic hydrogen production, it was revealed that the reaction pathways over TNRs-WQNDs (10) conformed to the Z-scheme theory. Finally, the fifth incessant cycled test indicated that TNRs-WQNDs (10) photoanode had excellent chemical stability and low photo-corrosion ability.

Reduced titania nanorods and Ni–Mo–S catalysts for photoelectrocatalytic water treatment and hydrogen production coupled with desalination

This study presents a ternary hybrid solar desalination process coupled with photoelectrocatalytic water treatment and H2 production in a single device. The desalination of brackish water in the desalination cell is initiated via photoinduced charge generation with a thermochemically reduced TiO2 nanorod array photoanode. The chlorides transferred to the neighboring anolyte at ion-transport efficiency of ∼100% are photoelectrochemically transformed into reactive chlorine species responsible for the decomposition of urea into nitrate in the anolyte. Simultaneously, the H2 production with a Ni–Mo–S (Ni2S3/MoS2) composite catalyst grown onto porous Ni substrate is achieved at Faradaic efficiency of ∼90% in the catholyte concentrated with desalted Na+. Regardless of the operation condition, the H2 energy contributes to the reduction in the energy consumption for desalination by 25%–30%. The overall ternary hybrid process is understood systematically, and the physiochemical properties and electrochemical behavior of the Ni–Mo–S catalysts are examined.

Superior photoelectrocatalytic performance of ternary structural BiVO4/GQD/g-C3N4 heterojunction

Herein, we performed an encyclopedic analysis on the photoelectrocatalytic hydrogen production of BiVO4/g-C3N4 decorated with reduced graphene oxide (RGO) or graphene quantum dots (GQDs). The differences between RGO and GQDs as an electron mediator was revealed for the first time in the perspective of theoretical DFT analysis and experimental validation. It was found that the incorporation of GQDs as an electron mediator promotes better photoelectrocatalytic hydrogen performance in comparison to the RGO. The addition of GQD can significantly improve the activity by 25.2 and 75.7% in comparison to the BiVO4/RGO/g-C3N4 and binary composite samples, respectively. Correspondingly, the BiVO4/GQD/g-C3N4 attained the highest photocurrent density of 19.2 mA/cm2 with an ABPE of 0.57% without the presence of any sacrificial reagents. This enhancement is stemming from the low photocharge carrier transfer resistance which was further verified via DFT study. The DFT analysis revealed that the BiVO4/GQD/g-C3N4 sample shared their electronic cloud density through orbital hybridization while the BiVO4/RGO/g-C3N4 sample show less mutual sharing. Additionally, the charge redistribution of the GQDs-composite at the heterostructure interface articulates a more stable and stronger heterojunction than the RGO-composite. Notably, this study provides new insights on the effect of different carbonaceous materials (RGO and GQDs) which are often used as an electron mediator to enhance photocatalytic activity.

Enhanced photoelectrocatalytic activity of Bi2S3–TiO2 nanotube arrays hetero-structure under visible light irradiation

Constructing heterosystems by sensitizing a wide band gap semiconductor with a narrow band gap semiconductor is an effective way to improve photocatalytic performance. Bismuth sulfide (Bi2S3) has a direct band gap of 1.38 eV and shows great potential in capturing visible light, which makes it a good candidate for photocatatlytic applications. In this work, Bi2S3 nanoparticles were efficiently deposited on TiO2 nanotube arrays (Bi2S3-TNTAs) by sequential chemical bath deposition (CBD) method to enhance visible light response of the photocatalytic system. Notably, a high-throughput screening method of scanning photoelectrochemical microscopy (SPECM) was exploited to evaluate photoelectrochemical response of the as-prepared composites and to find out the optimized photocatatlytic system. The effects of Bi2S3 nanoparticles on visible light absorption and photoelectrocatalytic hydrogen production rate of the TiO2-system were investigated in detail. When adopted as photoanode, the optimized heteroelectrode exhibited a more than 13-fold enhancement in hydrogen production rate. The result of electrochemical impedance spectroscopy (EIS) and photoluminescence (PL) shows that photo-generated charges excited under visible light in Bi2S3-TNTAs composites are efficiently separated, which gives rise to the superior photoelectrocatalytic performance of the Bi2S3-TNTAs photoanodes.

Photoelectrocatalytic hydrogen production of heterogeneous photoelectrodes with different system configurations of CdSe nanoparticles, Au nanocrystals and TiO2 nanotube arrays

The different configurations of CdSe nanoparticles, Au nanocrystals and TiO2 nanotube arrays play an important role in the photoelectrochemical behavior and photoelectrocatalytic hydrogen production of this heterogeneous photoelectrode system. It is discovered that the photoelectrocatalytic hydrogen production of the TiO2–CdSe–Au photoelectrode (1.724 mmol g−1 h−1) is about 4 times that of the TiO2–Au–CdSe photoelectrode (0.430 mmol g−1 h−1) under visible light irradiation. From the comprehensive investigation of their photoelectrochemical behaviors, it is illustrated that the interfacial electrical field has distinct effects on the separation and transportation of photogenerated carriers in these heterostructure photoelectrodes. The directions of the interfacial electrical fields formed at TiO2–Au and Au–CdSe interfaces are opposite in the TiO2–Au–CdSe photoelectrode, which hinders the separation of photogenerated electron-hole pairs and subsequent transportation of photogenerated carriers. On the contrary, the directions of the interfacial electrical fields formed at TiO2–CdSe and CdSe–Au interfaces are identical in the TiO2–CdSe–Au photoelectrode, which promotes the separation of photogenerated excitons and subsequently enhances their transportation for enlarged photocurrent density. The results of photoelectrocatalytic hydrogen production also confirm our assumption.

Nitrogen/Carbon-Coated Zero-Valent Copper as Highly Efficient Co-catalysts for TiO2 Applied in Photocatalytic and Photoelectrocatalytic Hydrogen Production.

Zero-valent copper (Cu0) is a promising co-catalyst in semiconductor-based photocatalysis as it is inexpensive and exhibits electronic properties similar to those of Ag and Au. However, its practical application in photocatalytic hydrogen production is limited by its susceptibility to oxidation, forming less active Cu species. Herein, we have carried out in situ encapsulation of Cu0 nanoparticles with N-graphitic carbon layers (14.4% N) to stabilize Cu0 nanoparticles (N/C-coated Cu) and improve the electronic communication with a TiO2 photocatalyst. A facile solvothermal procedure is used to coat the Cu0 nanoparticles at 200 °C, while graphitization is achieved by calcination at 550 °C under an inert atmosphere. The resultant N/C-coated Cu/TiO2 composites outperform the uncoated Cu counterparts, exhibiting a 27-fold enhancement of the hydrogen evolution rate compared to TiO2 and achieving a rate of 19.03 mmol g-1 h-1 under UV-vis irradiation. Likewise, the N/C-coated Cu co-catalyst exhibits a less negative onset potential of -0.05 V toward hydrogen evolution compared to uncoated Cu (ca. -0.30 V). This superior activity is attributed to coating Cu0 with N/C, which enhances the stability, electronic communication with TiO2, conductivity, and interfacial charge transfer processes. The reported synthetic approach is simple and scalable, yielding an efficient and affordable Cu0 co-catalyst for TiO2.

Hybrid 2D/3D g-C3N4/BiVO4 photocatalyst decorated with RGO for boosted photoelectrocatalytic hydrogen production from natural lake water and photocatalytic degradation of antibiotics

The photocharge carrier separation and migration within the heterostructure interface plays a pivotal role in the photoelectrocatalytic hydrogen production and the photocatalytic degradation activity. Herein, a series of the 2D/3D g-C3N4/BiVO4 photocatalyst decorated with RGO were successfully fabricated via a modified doctor blading technique. The as-developed 2D/3D RGO@ g-C3N4/BiVO4 photocatalysts were further evaluated for its bifunctional applications in photoelectrocatalytic hydrogen production and photocatalytic degradation of antibiotics (amoxicillin and ciprofloxacin). The optimized 1.2 wt% RGO@g-C3N4/BiVO4 photocatalyst demonstrated the maximum photoelectrocatalytic hydrogen production of 63.5 mmol/h with a photocurrent density of 14.44 mA/cm2 (ABPE of 0.41% at −0.05 V vs. Ag/AgCl). Concomitantly, the optimized as-developed photocatalysts were capable of degrading 91.9 and 84.3% amoxicillin and ciprofloxacin, respectively under visible-light illumination. The comprehensive kinetics and isotherms analysis revealed that the 1.2 wt% RGO@g-C3N4/BiVO4 photocatalyst obeyed the pseudo-first-order and Temkin models. In addition, the as-developed optimized photocatalyst was found to remain stable even after three cyclic activity with no obvious change in both photoelectrocatalytic and photocatalytic performance. This can be attributed to the synergistic interaction between RGO with the 2D/3D g-C3N4/BiVO4 photocatalyst which promotes robust interfacial contact at the heterostructure interface and allows smooth photocharge carrier transfer, results in limited recombination of the photocharge carriers. Finally, details of the photoelectrocatalytic and photocatalytic mechanisms were revealed along with the ciprofloxacin and amoxicillin degradation pathways.

Growth and characterization of PbI2-decorated ZnO nanowires for photodetection applications

In this study, we demonstrated for the first time the growth of ZnO nanowires (NWs) decorated with highly crystalline few-layer PbI2 and fabricated two-terminal single-nanowire photodetector devices to investigate the photoelectric properties of the hybrid nanostructures. We developed a novel two-step growth process for uniform crystalline PbI2 nanosheets via reactive magnetron deposition of a lead oxide film followed by subsequent iodination to PbI2 on a ZnO NW substrate, and we compared as-grown hybrid nanostructures with ones prepared via thermal evaporation method. ZnO–PbI2 NWs were characterized by scanning and transmission electron microscopy, X-ray diffraction analysis and photoluminescence measurements. By fabricating two-terminal single-nanowire photodetectors of the as-grown ZnO–PbI2 nanostructures, we showed that they exhibit reduced dark current and decreased photoresponse time in comparison to pure ZnO NWs and have responsivity up to 0.6 A/W. Ab initio calculations of the electronic structure of both PbI2 nanosheets and ZnO NWs have been performed, and show potential for photoelectrocatalytic hydrogen production. The obtained results show the benefits of combining layered van der Waals materials with semiconducting NWs to create novel nanostructures with enhanced properties for applications in optoelectronics or X-ray detectors.

UiO-67 metal-organic gel material deposited on photonic crystal matrix for photoelectrocatalytic hydrogen production.

Robust UiO-67 metal–organic framework nanoparticles have been precisely and uniformly anchored on the surface of a photonic crystal via metal–organic gelation, resulting in a nanoscale UiO-67 composite. Mott–Schottky measurements indicate that UiO-67/B is an n-type semiconductor with electron conduction, and the band gap significantly decreases with the assistance of the photonic crystal matrix with a band gap of 0.75 eV. Benefiting from the abundant photoelectrons trapped from the photonic crystal, good hydrogen evolution reaction performance is achieved under light irradiation. The current density increases from 3.2 to 7.0 mA cm−2 at −0.6 V (vs. RHE) for UiO-67/B. The optimized carrier density obtained from UiO-67/B is apparently increased 2.15 times under light irradiation for 30 min. This work provides a rational strategy to address the photo-capture and energy transfer issues of metal–organic frameworks under visible light irradiation for H2 production in artificial photosynthesis.

Photoelectrocatalytic Hydrogen Production Using a TiO2/WO3 Bilayer Photocatalyst in the Presence of Ethanol as a Fuel

Photoelectrocatalytic hydrogen production was studied by using a photoelectrochemical cell where the photoanode was made by depositing on FTO electrodes either a nanoparticulate WO3 film alone or a bilayer film made of nanoparticulate WO3 at the bottom covered with a nanoparticulate TiO2 film on the top. Both the electric current and the hydrogen produced by the photoelectrocatalysis cell substantially increased by adding the top titania layer. The presence of this layer did not affect the current-voltage characteristics of the cell (besides the increase of the current density). This was an indication that the flow of electrons in the combined semiconductor photoanode was through the WO3 layer. The increase of the current was mainly attributed to the passivation of the surface recombination sites on WO3 contributing to the limitation of charge recombination mechanisms. In addition, the top titania layer may have contributed to photon absorption by back scattering of light and thus by enhancement of light absorption by WO3. Relatively high charge densities were recorded, owing both to the improvement of the photoanode by the combined photocatalyst and to the presence of ethanol as the sacrificial agent (fuel), which affected the recorded current by “current doubling” phenomena. Hydrogen was produced under electric bias using a simple cathode electrode made of carbon paper carrying carbon black as the electrocatalyst. This electrode gave a Faradaic efficiency of 58% for hydrogen production.