Composite Photocathode Research Articles

Graphene Intermediate Layer for Robust and Spectrum-Extended Cu Photocathode Activated with Cs and O.

Developing an effective method to stably enhance the quantum efficiency (QE) and extend the photoemission threshold of Cu photocathodes beyond the ultraviolet region could benefit the photoinjector for ultrafast electron source applications. The implementation of a 2D material protective layer is considered a promising approach to extending the operating lifetime of photocathodes. We propose that graphene can serve as an intermediate layer at the interface between photocathode material and low-work-function coating. The role of oxygen in the Cs/O activation process on the Cu surface is altered by the graphene interlayer. Besides, the few-layer graphene (FLG) surface could be more likely to induce the formation of Cs2O. Thus, the graphene-Cu composite photocathode can achieve an ultralow surface work function of down to 0.878 eV through Cs/O activation. The photoemission performance of the composite cathode with a FLG interlayer is significantly enhanced. The photocathode has an extended spectral response to the near-infrared region and a higher QE. At 350 nm, its QE is more than twice that of the cesiated bare Cu, reaching 0.247%. After degradation, the graphene-Cu cathode can be fully restored by reactivation, with remarkably enhanced stability. In addition, the composite cathode can be operated reliably under a poor vacuum pressure of over 4 × 10-6 Pa. This study validates a new method for incorporating 2D materials into photocathodes, offering novel approaches to explore robust and spectrum-extended photocathodes.

Sludge reduction and hydrogen production in a microbial photoelectrochemical cell with a g-C3N4/CQDs/BiOBr composite photocathode

ABSTRACT Hydrogen (H2) remains a pivotal clean energy source, and the emergence of Solar-powered Microbial Photoelectrochemical Cells (MPECs) presents promising avenues for H2 production while concurrently aiding organic matter degradation. This study introduces an MPEC system employing a g-C3N4/CQDs/BiOBr photocathode and a bioanode, successfully achieving simultaneous H2 production and sludge reduction. The research highlights the effective formation of a Z-type heterojunction in the g-C3N4/CQDs/BiOBr photocathode, substantially enhancing the photocurrent response under light conditions. Operating at – 0.4 V versus RHE, it demonstrated a current density of – 3.25 mA·cm−2, surpassing that of g-C3N4/BiOBr (−2.25 mA·cm−2) by 1.4 times and g-C3N4 (−2.04 mA·cm−2) by 1.6 times. When subjected to visible light irradiation and a 0.8 V applied bias voltage, the MPEC system achieved a current density of 1.0 mA·cm−2. The cumulative H2 production of the MPEC system reached 8.9 mL, averaging a production rate of 0.13 mL·h−1. In the anode chamber, the degradation rates of total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total suspended solids (TSS), volatile suspended solids (VSS), proteins, polysaccharides, and volatile fatty acids (VFA) in the sludge were recorded at 57.18%, 82.64%, 64.98%, 86.39%, 42.81%, 67.34%, and 29.01%, respectively.

Photo-assisted enhancement of lithium-ion battery performance with a LiFePO4/TiO2 composite cathode

The development of photo-assisted lithium-ion batteries (P-LIBs) holds immense promise for enhancing battery performance and enabling self-charging capabilities. However, the realization of these transformative devices hinges on the creation of novel photoelectrodes with exceptional light absorption and electrochemical properties. In this study, we introduce a composite photocathode composed of TiO2 and LiFePO4, demonstrating remarkable dual functionality for light-to-electricity conversion and energy storage. Comparative analysis reveals substantial improvements in the charge/discharge capacity of P-LIBs under sunlight, with enhancements of 6.6 % and 4.6 % at a 0.5 C rate. Our findings attribute these performance gains to rapid Li+ conduction, facilitating complete valence state transitions between Fe2+ and Fe3+ under sunlight conditions. This work paves the way for significant advancements in photoelectrode design for P-LIBs.

Enhanced photocathode performance and stability for solar-powered hydrogen production through SiNWs@NC composite

Solar-powered photoelectrochemical hydrogen production has received garnered significant attention, yet the development of efficient, stable, and cost-effective photocathodes remains a formidable challenge. In this study, we achieved a breakthrough by fabricating a SiNWs@NC composite photocathode through a straightforward electrodeposition and calcination process. Notably, the incorporation of nitrogen-doped carbon as a co-catalyst not only facilitated efficient electron transfer within the photocathodes, but also serves as a protective layer, effectively mitigating the photocorrosion of SiNWs and enhancing overall stability. Under a bias voltage of −0.85 V vs. RHE and visible light irradiation, the SiNWs@NC electrode exhibited exceptional performance, achieving a peak photocurrent density of 25.41 mA·cm−2 and an ABPE efficiency and 8.8 %. This pioneering work presents a promising solution for photocatalytic hydrogen production, highlighting the advantages of its facile preparation, superior photovoltaic performance, and remarkable stability.

High time-resolution MRPC detector for TOF-PET

The traditional TOF-PET (Positron emission tomography) mainly uses the structure of a scintillator detector connected to a photomultiplier tube. The structure has the disadvantages that time resolution is not good enough (about 300 ps FWHM) for improving the signal-to-noise ratio of the acquisition system, which is not conducive to the detection of microtumors in the clinic and reduction in imaging time. The thickness of the scintillator is large (greater than 3 cm). Traditional PET has low geometric efficiency and sensitivity. It requires a long time to complete a full-body scan. However, the MRPC can be made into a 2.4-meter-long whole body PET. The high cost of traditional TOF-PET limits its widespread use in medical and other fields. The excellent time resolution of MRPC makes MRPC TOF-PET a good application prospect. This paper shows the time resolution of two 32-gap MRPCs with 128μm gap thickness on cosmic rays and 0.511 MeV photons. By using the fast front-end amplifier and waveform acquisition system, the time resolution for cosmic rays is 27 ps and the rms time accuracy per 0.511 MeV photon is 72 ps. The time resolution in terms of FWHM of the time difference between photon pairs is 239 ps FWHM. The reason why MRPC detectors have different time resolutions for cosmic rays and 0.511 MeV photons is related to the different ways different particles act and the thickness of the detector. We propose to use a Cerenkov radiator to convert gamma into ultraviolet photons and use a composite photocathode to detect, improving the detection efficiency to 6.4% for RPC.

Photo-rechargeable battery with an energetically aligned beetroot Dye/Cl-Graphene quantum dots/MoO3 nanorods composite

A stand-alone, low-cost non-aqueous photo-rechargeable zinc ion battery configuration is presented. The photo-battery integrates the functions of energy conversion and storage in a single device thus minimizing space and material requirements as well as cost. The cell is based on a photocathode with TiO2 and MoO3-nanorods (NRs) as the storage layers, with additional roles of electron transport layer and photosensitizer for TiO2 and MoO3 respectively. Photoactive beetroot (BT) dye and Cl-doped graphene quantum dots (GQDs) were also incorporated therein to yield the TiO2/BT/Cl-GQDs/MoO3-NRs composite photocathode for broad spectral utilization. Under irradiance, the BT dye, Cl-GQDs and MoO3 undergo electron-hole separation, channel the electrons to the external circuit via TiO2 through aligned energy levels and simultaneously charge the battery to ∼1 V, without the application of any external bias or current. The photo-charging and discharge capacities of the photo-battery: TiO2/BT/Cl-GQDs/MoO3-NRs/Zn2+/Zn-AC in the biased mode under an applied current density of 21 mA g−1 and under 1 sun irradiance (100 mW cm−2, AM 1.5 G) are 104 mAh g−1 and 240 mAh g−1 respectively. The photo-charging capacity under 1 sun irradiance in the unbiased mode is ∼75 mAh g−1. A Zn-activated carbon composite (derived from lemon pieces) as the anode electro-catalyzes the reduction of Zn2+ during photo-charging, leading to a power conversion efficiency of 4.03 % under one sun illumination. This has a cycle life of 200 cycles and offers a constant photocurrent of 8.3 mA cm−2 with a hold time of more than 100 s under irradiance which can easily charge any small electronic device. It is an economically viable configuration with huge technological potential for possible commercialization.

Van Der Waals Heterojunction Modulated Charge Collection for H2O2 Production Photocathode

AbstractEfficient photocarrier generation and collection are highly desirable for solar‐fuel conversion systems. However, the latter is challenging for many photoelectrodes due to carrier losses happening in the semiconductor‐electrolyte interface and the semiconductor‐substrate interface. To overcome it, a novel Au/CuBi2O4 (CBO)/PtSe2 van der Waals heterojunction photocathode has been developed to boost photocarrier collection. As a result, the ohmic contact at Au/CBO interface shows a low resistance for hole transfer. Meanwhile, while promoting electron transfer, the Van der Waals heterojunction of CBO/PtSe2 interface with energy barrier‐blocked holes. Concurrently, the composite photocathode exhibits significantly enhanced performance: a photocurrent of −0.59 mA cm−2 at 0.5 V versus reversible hydrogen electrode and an H2O2 generation rate of 2.39 mol (Lhm2)−1. This work demonstrates the charge regulation role of Van der Waals heterojunctions in the solar‐fuel system. More broadly, Van der Waals heterojunctions provide an excellent bond‐free approach to creating versatile optoelectronic devices.

FeOOH decorated Sb2Se3@CdxZn1-xS core-shell nanorod heterostructure photocathode for enhancing photoelectrochemical performance

In this work, a core-shell heterostructure Sb2Se3@CdxZn1-xS photocathode was constructed on the Fluorine-doped Tin Oxide (FTO) by Vapor Transport Deposition (VTD) and hydrothermal method, then β-FeOOH was deposited on the surface of Sb2Se3@Cd0.8Zn0.2S. The investigation indicates that Sb2Se3@CdxZn1-xS has a one-dimensional (1D) nanorod structure, which can provide a fast carrier transmission channel. The introduction of a CdxZn1-xS shell can accelerate the charge separation of Sb2Se3 and type-II heterojunction between them can enhance the electron migration efficiency of Sb2Se3. Using β-FeOOH as the protective layer can not only protect the ternary photocathode from photocorrosion, but also act as a cocatalyst to enhance surface reaction kinetics. Photoelectrochemical (PEC) tests found that the composite photocathode Sb2Se3@Cd0.8Zn0.2S/β-FeOOH achieves a higher photocurrent density (0.252 mA/cm2), which is about 21 times higher than that of pure Sb2Se3 nanorod photocathode (0.012 mA/cm2) under the same condition, besides, it also exhibited more excellent stability during 1 h hydrogen production. This work provides an effective way to design and fabrication of nanostructures for high-efficiency water splitting photoelectrodes.

Gold-Promoted Electrodeposition of Metal Sulfides on Silicon Nanowire Photocathodes To Enhance Solar-Driven Hydrogen Evolution.

Constructing composite structures is the key to breaking the dilemma of slow reaction kinetics and easy oxidation on the surface of lightly doped p-type silicon nanowire (SiNW) array photocathodes. Electrodeposition is a convenient and fast technique to prepare composite photocathodes. However, the low conductivity of SiNWs limits the application of the electrodeposition technique in constructing composite structures. Herein, SiNWs were loaded with Au nanoparticles by chemical deposition to decrease the interfacial charge transfer resistance and increase active sites for the electrodeposition. Subsequently, co-catalysts CoS, MoS2, and Ni3S2 with excellent hydrogen evolution activity were successfully composited by electrodeposition on the surface of SiNWs/Au. The obtained core-shell structures exhibited excellent photoelectrochemical hydrogen evolution activity, which was contributed by the plasma property of Au and the abundant hydrogen evolution active sites of the co-catalysts. This work provided a simple and efficient solution for the preparation of lightly doped SiNW-based composite structures by electrodeposition.

Simultaneous removal of Cr(VI) and phenol in a dual-chamber photocatalytic microbial fuel with NiCo2O4/MoS2/GF photocathode

Efficient treatment and resource utilization of sewage are of great value for global sustainability. In this study, a composite photocathode was prepared by loading NiCo2O4 nanosheets and MoS2 nanoflowers to a graphite felt (GF)-based electrode through a two-step hydrothermal and calcination method. A photocatalytic microbial fuel cell (PMFC) was constructed using the NiCo2O4/MoS2/GF photocathode and carbon felt (CF) anode in a dual-chamber H-type battery. Cr(VI) and phenol were employed as target pollutants in the cathode chamber. The photoelectric performance of the NiCo2O4/MoS2/GF photocathode and the removal efficiency of the battery system were studied systematically. When a mixed solution of Cr(VI) and phenol was used, the removal rates of Cr(VI) and phenol after 24 h of light exposure were 8.13 % and 12.65 % higher than those when Cr(VI) or phenol was used alone, respectively. At the same time, the output power density of the battery in the mixed pollutants was 362.7 mW/m3, which was 45.78 % higher than that in the single Cr(VI) solution (248.8 mW/m3). The excellent performance of the PMFC was attributed to three reasons: (1) NiCo2O4 and MoS2 were simultaneously excited as two narrow-bandgap semiconductors, and the utilization rate of light energy was increased; (2) The Z-scheme heterojunction between NiCo2O4 and MoS2 improved the separation efficiency of the photoelectric carriers and retained the high valence band of NiCo2O4 and low conduction band of MoS2 to the greatest extent, which is crucial for the PMFC to achieve electronic export and double contaminant removal; and (3) the NiCo2O4 nanosheet and MoS2 nanoflower structures enhanced the contact between the catalysts and the pollutants.

A 3D-printed freestanding graphene aerogel composite photocathode for high-capacity and long-life photo-assisted Li-O2 batteries.

The construction of a high-performance photocathode is essential for improving Li-O2 battery performance and solar energy utilization. However, the single pore and few active reaction sites of the photocathode result in insufficient discharge capacity and unsatisfactory cycling durability. Herein, we designed and fabricated a self-standing 3D-printed multi-pore graphene-based photocathode via direct ink writing (DIW) featuring non-competitive three-phase transmission channels to promote the transport of Li+, e-, and O2. The macropore provides adequate space for storage of the Li2O2 discharge product; the mesopore facilitates the reactant transport, while the micropore stores the active ions. Furthermore, the photogenerated carriers of the photocathode promote overpotential reduction. Under illumination, the charging voltage of the Li-O2 battery with a reduced graphene oxide/titanium dioxide (rGO/TiO2) photocathode is decreased from 4.55 V to 3.77 V, and the battery exhibits stable cycling for 1000 hours. Notably, the photocathode's pore structure and specific surface area are further optimized after adding carbon nanotubes (CNTs). Compared with rGO/TiO2, the specific surface area of reduced graphene oxide/titanium dioxide/carbon nanotubes (rGO/TiO2/CNTs) is increased by 12 times to 194.13 m2 g-1, and the discharge capacity can reach up to 33.37 mA h cm-2. This self-standing 3D-printed photocathode structure paves a new way for developing high-performance energy storage systems.

Boosting photocarrier collection in semiconductors by synergizing photothermoelectric and photoelectric

Efficient generation and collection of photocarriers is a contradiction for most metal oxide semiconductors. An approach to better understanding and controlling photocarriers’ special collection is critical for solar-fuel conversation. Herein, p-type BiFeO3 was chosen to reveal the diffusion length (∼34 nm) limited performance and to develop an approach to boosting photocarrier collection by synergizing photothermoelectric and photoelectric. In this approach, efficient photocarrier collection was realized by two processes: 1) an inner photothermoelectric voltage as the carriers’ driving force to promote drift in the flat band region; 2) the accumulated electrons in the cooling interface consumed photogenerated holes and inhibited recombination. As a result, the composite photocathode shows a state-of-the-art photocurrent of − 0.49 mA·cm−2 and an H2O2 generation rate of 695 mmol/(L·m2). This work aims to provide a broader understanding of photocarrier collection's limited performance of metal oxide photoelectrode and explore a universal approach to improving it without extra power input.

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.

Facile synthesis of BiFeO3/Bi2O3 composite photocathode with improved photoelectrochemical performance

BiFeO3-based ferroelectrics are promising photoelectrodes for photoelectrochemical (PEC) water splitting. To further enhance its photoelectrocatalytic activity, BiFeO3/Bi2O3 composite is designed by a simple and cost-effective flame annealing process in this work. The obtained BiFeO3/Bi2O3 photocathode achieves a photocurrent density of −0.21 mA/cm−2 at 0.38 VRHE, with a 160 mV positive shift of the onset potential. Furthermore, the photon-to-current efficiency of BiFeO3/Bi2O3 displays an obvious enhancement. The improved PEC performance is due to the formation of composite, which reduces the recombination of carriers, promotes interfacial charge transfer and provides more active sites. Our work provides a promising approach to improve the performance of ferroelectric photoelectrodes.

Visible-light enhanced azo dye degradation and power generation in a microbial photoelectrochemical cell using AgBr/ZnO composite photocathode

In this study, a dual-chamber microbial photoelectrochemical cell (MPEC) composed of a bio anode and a photoresponse AgBr/ZnO-modified graphite as a photocathode was investigated. The cell efficacy in degrading reactive black 5 (RB5), a diazo dye, in the cathodic chamber and simultaneously, electricity generation was analyzed. The synthesized AgBr/ZnO photocatalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (UV-vis DRS), photoluminescence (PL), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). Under light irradiation, the MPEC equipped with AgBr/ZnO-modified photocathode yielded 61% RB5 dye degradation over 72 h which indicated a highly enhanced performance compared with the irradiated bare graphite (11.74%). Besides, the maximum power density produced was 53.8 mW m−2 under visible light illumination and 32.5 mW m−2 in dark conditions. The MPEC reported in this research seems to be a promising system for bioelectricity generation, wastewater treatment in the anodic chamber, and also, dye pollutant degradation in the cathodic chamber.

TiO2/CdS composite photocathode improves the performance and degradation of wastewater in microbial fuel cells.

Optimization of dye decolourization for wastewater and power production are explored in dual-chamber microbial fuel cells (MFCs) with TiO2/CdS photocathodes. The rapid reduction of azo dye methylene blue (MB) and power production were enhanced with TiO2/CdS photocathode under illumination. The analysis of electrochemical impedance spectra indicated that the photocatalysis of TiO2/CdS accelerated the electron transfer process of photoelectrode reduction. Moreover, the UV-visible light spectrophotometer showed that the maximum degradation of the MFCs was 98.25%, which illustrated that MB may be cleaved by photoelectrons generated by light irradiation on the illuminated TiO2/CdS photocathode. Finally, the power production of MFCs in this work promoted reductive decolourization of the dye MB solution.

P25-induced polydopamine conformal assembly on Cu2O polyhedra for hydrophilic and stable photoelectrochemical performance

The hydrophilic Cu2O/PDA/P25 composite photocathode has outstanding PEC water reduction performance.

Plasmonic Ag-decorated Cu2O nanowires for boosting photoelectrochemical CO2 reduction to multi-carbon products.

The generation of multi-carbon products on the Cu2O photocathode remains a great challenge. Herein, effective charge separation and surface catalytic reaction are achieved for photoelectrochemical CO2 reduction through plasmon metal (Ag) decoration on Cu2O nanowires. The Cu2O/Ag composite photocathode achieves a 47.7% faradaic efficiency for CH3COOH and the generation rate is 212.7 μmol cm-2 h-1 under illumination, which is about five times that in dark (44.4 μmol cm-2 h-1) at -0.7 V vs. RHE.

CuBi2O4 photocathode with integrated electric field for enhanced H2O2 production

Metal oxide semiconductors are promising for photosynthetic H2O2 production, provided the issue of excessive charge recombination can be adequately addressed. Inducing internal electric field is a common remedial strategy to inhibit carrier recombination but challenging to accomplish without external power input. To overcome this drawback, a novel photocathode was designed and fabricated by combing photothermoelectricity and photoelectricity by adding a NaCo2O4 film under the CuBi2O4 film to generate an internal electric field from photoinduced temperature gradients. Our results show the significantly enhanced photoelectrochemical activity for the composite photocathode with an H2O2 production concentration of 192.9 µmol/L, 2.4 times higher than CuBi2O4. Photocurrent under controlled temperature gradients and COMSOL simulation defined that the enhancement comes from the synergy of photothermoelectricity and photoelectricity. This work demonstrates a feasible strategy to inhibit carrier recombination in photoelectrode with internal thermoelectric potential, which can significantly enhance the energy conversion efficiency without extra energy consumption.

Ameliorating Cu2+ reduction in microbial fuel cell with Z-scheme BiFeO3 decorated on flower-like ZnO composite photocathode

BiFeO3 nanoparticle decorated on flower-like ZnO (BiFeO3/ZnO) was fabricated through a facile hydrothermal-reflux combined method. This material was utilized as a composite photocathode for the first time in microbial fuel cell (MFC) to reduce the copper ion (Cu2+) and power generation concomitantly. The resultant BiFeO3/ZnO-based MFC displayed distinct photoelectrocatalytic activities when different weight percentages (wt%) BiFeO3 were used. The 3 wt% BiFeO3/ZnO MFC achieved the maximum power density of 1.301 W m−2 in the catholyte contained 200 mg L−1 of Cu2+ and the power density was greatly higher than those pure ZnO and pure BiFeO3 photocathodes. Meanwhile, the MFC exhibited 90.7% removal of Cu2+ within 6 h under sunlight exposure at catholyte pH 4. The addition of BiFeO3 nanoparticles not only manifested outstanding capability in harvesting visible light, but also facilitated the formation of Z-scheme BiFeO3/ZnO heterojunction structure to induce the charge carrier transfer along with enhanced redox abilities for the cathodic reduction. The pronounced electrical output and Cu2+ reduction efficiencies can be realized through the synergistic cooperation between the bioanode and BiFeO3/ZnO photocathode in the MFC. Furthermore, the developed BiFeO3/ZnO composite presented a good stability and reusability of photoelectrocatalytic activity up to five cyclic runs.