Photocurrent Measurements Research Articles

Carrier trapping in diamond Schottky barrier diode

Carrier trapping in a diamond Schottky barrier diode, consisting of a stack of a p− drift and p+ contact layer, is experimentally studied via subgap photocurrent measurements. In the measurements, trapped carriers are detected as an increment of the diode current under a probe light illumination in a near infrared range of 2.0 μm (0.62 eV). The density of trapped carriers is examined, and it is found to be sufficiently low, compared with that of free carriers, by an order of 105. Interestingly, the trapped carriers are observed only for the forward bias of the diode; they are not observed for the reverse bias. This suggests that the carrier trapping, yielding trapped carriers, originates from the valence band offset at the p−/p+ interface.

Effect of sub-bandgap defects on radiative and non-radiative open-circuit voltage losses in perovskite solar cells

The efficiency of perovskite solar cells is affected by open-circuit voltage losses due to radiative and non-radiative charge recombination. When estimated using sensitive photocurrent measurements that cover the above- and sub-bandgap regions, the radiative open-circuit voltage is often unphysically low. Here we report sensitive photocurrent and electroluminescence spectroscopy to probe radiative recombination at sub-bandgap defects in wide-bandgap mixed-halide lead perovskite solar cells. The radiative ideality factor associated with the optical transitions increases from 1, above and near the bandgap edge, to ~2 at mid-bandgap. Such photon energy-dependent ideality factor corresponds to a many-diode model. The radiative open-circuit voltage limit derived from this many-diode model enables differentiating between radiative and non-radiative voltage losses. The latter are deconvoluted into contributions from the bulk and interfaces via determining the quasi-Fermi level splitting. The experiments show that while sub-bandgap defects do not contribute to radiative voltage loss, they do affect non-radiative voltage losses.

Fabrication and Electrical Characterization of p/n PbSe Diodes

Lead selenide (PbSe) diodes were fabricated using a magnetron sputtering process system with a pulsed DC power supply and a 2-inch PbSe target with a purity of 5N. For p-type PbSe thin films, the process variable was the oxygen ratio in the mixed gas of argon and oxygen. The electrical characteristics of the thin films were observed after heat treatment. For the n-type PbSe, nickel (Ni) was used as a doping material. The deposition and doping were performed simultaneously using a co-sputtering method. During co-sputtering, the input power of the Ni sputter gun was adjusted as a process variable. Hall measurement experiments were performed to measure the doping concentration and resistivity of both the p-type and n-type PbSe semiconducting films. The maximum doping concentration was 2.33×10<sup>19</sup> cm<sup>-3</sup> for p-type PbSe and 7.55×10<sup>20</sup> cm<sup>-3</sup> for n-type PbSe thin films, respectively. The p-n junction IV curve showed that the lowest forward voltage generation point, V<sub>f</sub>, was 1.5 V and the reverse breakdown voltage was -4.3 V. In the photocurrent measurement, the photo sensitivities of the heat-treated samples were higher than that of the non-treated sample, and the maximum value was 5.148. Photo responsivity was also higher in the heat-treated samples. Its maximum was 0.7306 mA / W.

Facile construction of multifunctional xNiCo2O4/BiVO4 heterojunction with accelerated charge transfer for efficient photocatalytic treatment of Cr (VI), MB and TC under visible light

The release of industrial effluents, comprising of organic dyes, antibiotics, and heavy metals poses substantial environmental and ecological threats. Among the different approaches, the utilization of heterogeneous photocatalysis based on semiconducting metal oxides is of paramount important to removal of organic ( MB dye and TC antibiotic) and inorganic pollutants ( Cr (VI) ) in wastewater. In this work, a new approach for creating type-II heterojunction photocatalysts named xNiCo2O4/BiVO4 or BNC is suggested. The as-prepared samples were thoroughly examined by means of several sophisticated analytical tools to investigate their physicochemical properties. These composites were utilized in the decomposition of MB dye, TC drug and the reduction of Cr (VI) under visible light irradiation. According to the findings, the creation of type-II heterojunction at BiVO4–NiCo2O4 interface greatly improved charge transportation while successfully preventing electron-hole recombination. Among the various composites studied, BNC-2 demonstrated an enhanced photocatalytic activity towards degradation of MB and TC, which were found to be 91 % over a period of 150 min and 95 % within only 60 min, respectively. Moreover, the photocatalytic reduction of Cr (VI) was accomplished 96 % within just 25 min. Additionally, it is discovered that BNC-2 displayed promising photostability and recyclability with a retention of >90 % after five consecutive cycles. The enhanced photocatalytic activity of BNC-2 is evidently attributed to the expedited separation and transfer of charges, as proven by photocurrent measurement, photoluminescence and electrochemical impedance spectroscopy analyses. Hence, the current amalgamation of NiCo2O4 and BiVO4 heterojunction composite has paved novel paths towards photocatalytic removal of organic as well as inorganic contaminants.

Stable photocurrent–voltage characteristics of perovskite single crystal detectors obtained by pulsed bias

Photocurrent–voltage characterization is a crucial method for assessing key parameters in x-ray or γ-ray semiconductor detectors, especially the carrier mobility lifetime product. However, the high biases during photocurrent measurements tend to cause severe ion migration, which can lead to the instability and inaccuracy of the test results. Given the mixed electronic–ionic characteristics, it is imperative to devise novel methods capable of precisely measuring photocurrent–voltage characteristics under high bias conditions, free from interference caused by ion migration. In this paper, pulsed bias is employed to explore the photocurrent–voltage characteristics of MAPbBr3 single crystals. The method yields stable photocurrent–voltage characteristics at a pulsed bias of up to 30 V, proving to be effective in mitigating ion migration. Through fitting the modified Hecht equation, we determined the mobility lifetime products of 1.0 × 10−2 cm2⋅V−1 for hole and 2.78 × 10−3 cm2⋅V−1 for electron. This approach offers a promising solution for accurately measuring the transport properties of carriers in perovskite.

Pressure-induced photo-responsiveness enhancement and positive–negative switch in Bi2S3

Bi2S3 has attracted significant interest due to its unique optical, electrical, and photosensitive properties. The utilization of pressure has been substantiated as a proficient technique in modulating the optoelectronic characteristics of functional materials and has garnered increasing attention. In this work, the photoresponse of Bi2S3 upon compression was systematically investigated in combination with in situ photocurrent measurements, Raman spectroscopy, absorption spectroscopy, and density functional theory calculations. Under pressure, Bi2S3 exhibits two distinct photoresponses. Bi2S3 exhibits an obvious positive photoresponse in the pressure range from 0.5 to 9.7 GPa. The photocurrent shows a rapid increase with increasing pressure and reaches the maximum value at 4.0 GPa, which is 5.6 times of the initial value. Interestingly, above 30.3 GPa, Bi2S3 shows a negative photocurrent response, which can be attributed to the photothermal effect caused by pressure-induced metallization phase transition. Our findings provide insight into the modulation of the optoelectronic properties of Bi2S3 and offer more possibilities in the further optimizing design optoelectronic devices based on Bi2S3.

Enhanced organic pollutant and AOX degradation of lignin-biochar/ZnAl2O4/BiPO4 with adsorption-photocatalysis synergy: Roles of lignin-biochar

In this work, lignin-biochar (LC)/ZnAl2O4/BiPO4 with adsorption and photocatalysis synergy were fabricated through hydrothermal process. The roles of lignin-biochar on the crystalline structure, shape and photoelectrochemical capacities of LC/ZnAl2O4/BiPO4 were carried out by X-ray power diffractometer pattern (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffusion reflectance spectra (UV–Vis DRS), photoluminescence spectra (PL), transmission electron microscope (TEM), scanning electron microscope (SEM), electrochemical impedance and transient photocurrent measurements. Photocatalytic experiment showed that the adsorption and photocatalytic efficiencies of ZnAl2O4/BiPO4 were greatly boosted with the introduced lignin-biochar, which is owing to its higher surface specific area, larger aromatic ring structure and superior electron transmission capacity. The highest kinetic constant of LC/ZnAl2O4/BiPO4 on the MB degradation is 2.1342 h−1 under UV illumination, increased by 5.52-fold for BiPO4 and 2.23-fold for ZnAl2O4/BiPO4, respectively. Meanwhile, the LC/ZnAl2O4/BiPO4 composites display excellent performance in the bamboo pulp bleaching wastewater treatment, and the CODCr and AOX removals of the wastewater are 65.2 % and 69.2 %, respectively. The lignin-biochar in the composites can not only enhance the adsorption of pollutant in the wastewater, but accept the photo-generated electrons from the semiconductor, leading to an enrichment of the pollutant and accelerated separation of electrons-holes pairs, ultimately enhancing the photocatalytic activities. The superior adsorption and photocatalytic efficiency of lignin-biochar-based composite makes it a promising candidate for the elimination of refractory pollutant in the industrial wastewater.

Effect of the Heterovalent Sc3+ and Nb5+ Doping on Photoelectrochemical Behavior of Anatase TiO2

In this study, we explored the effect of either Nb or Sc doping at a concentration range of 0.0–1.0 at.% on the physical–chemical and photoelectrochemical behavior of TiO2 anatase electrodes. This behavior was characterized by work function, flat band potential, donor density, spectral dependence of photocurrent and stationary photocurrent measurements. All experimental results are interpreted in terms of the formation of the shallow delocalized polaron states in the case of Nb doping and deep acceptor states induced by Sc doping on TiO2 anatase.

Stability and gap states of amorphous In-Ga-Zn-Ox thin film transistors: Impact of sputtering configuration and post-annealing on device performance

Stability of amorphous In-Ga-Zn-Ox (a-IGZO) thin-film-transistors (TFTs) is studied from a viewpoint of gap states, associated with oxygen-related defects and structural disordering. The a-IGZO gap states are controlled through the film preparation by magnetron sputtering under two different configurations and post-annealing in oxygen atmosphere. The distribution of gap states is then evaluated from the subgap absorption spectrum, which is measured by a constant photocurrent measurement technique. With this known distribution, a-IGZO TFTs are fabricated, and the stability of the TFT performances is examined through the negative bias induced stability (NBIS) experiments. The results suggest that a negative threshold voltage shift, induced by NBIS, is improved by reducing the density of gap states, i.e., narrowing the gap state distribution. The reduction of gap states also contributes to the improvement of subthreshold swing.

Dynamics and impurity spectral characteristics of coaxial gun discharge plasma

<sec>The coaxial gun discharge can produce plasma jet with high velocity, high density and high energy density, and has extensive applications, such as in plasma space propulsion, simulation of the interaction between edge local mode and wall materials in ITER, fuel injection in magnetic confinement fusion devices, and laboratory astrophysics. In the pre-filled discharge mode or snowplow mode, the plasma current sheet is formed near the insulating layer surface and moves toward the end of the coaxial gun under Lorentz force. Plasma velocity, density and purity characteristics are very important research contents for the actual applications of coaxial gun. Emission spectrometry as a non-interference method can be used to diagnose a variety of plasma physical properties.</sec><sec>In this experiment, the effects of different discharge currents and gas pressures on the plasma dynamics, electron density and impurity emission spectra of coaxial gun discharge plasma are studied through the measurement of plasma photocurrent, emission spectra and the shooting of discharge images. The experimental results show that the acceleration time of the plasma in the gun decreases with current increasing in a range of 30–70 kA when the gas pressure is 10 Pa, the spectral intensity of anode and cathode impurities in plasma increase with current amplitude increasing. When the discharge current is 40 kA and the gas pressure is in a range of 10–70 Pa, the acceleration time of plasma increases with gas pressure rising, and the spectral intensity of the cathode impurity in the plasma decreases with the pressure increasing, while the spectral intensity of the anode impurity increases gradually, but its growth rate decreases continuously. The analysis indicates that the presence of metallic impurities originating from the electrode material limits the jet velocity of the plasma and is the main cause of the deviation from theoretical value. The plasma pinch effect at the nozzle of coaxial gun and the acceleration time of high-density arc in the gun are important factors affecting anode ablation. The impurity of cathode material is produced by ion bombardment sputtering, which mainly depends on the energy carried by ions. Therefore, a reasonable choice for discharge parameters is the key factor to obtain optimal plasma characteristics during the discharge of the coaxial gun.</sec>

Photocatalytic activity of a 2D copper porphyrin metal-organic framework for visible light overall water splitting.

A 2D copper tetrakis(4-carboxyphenyl)porphyrin metal-organic framework has been prepared and used as a photocatalyst for overall water splitting, measuring under visible light irradiation (λ > 450 nm) under one sun power conditions a H2 production rate of 120 μmolH2 gcatalyst -1 h-1 that is among the highest ever reported. While the 2D Cu porphyrin MOF undergoes substantial degradation in 3 h upon UV irradiation (320-380 nm) in the presence of air, it appears to be photostable under the conditions of the overall water splitting and visible light exposure, exhibiting similar temporal profiles for H2 and O2 evolution. Photocurrent experiments and band energy measurements indicate that the photocatalytic efficiency derives from an efficient charge separation in the visible region (apparent electron charge extraction efficiency at 540 nm of 0.1%) and adequate alignment of the redox potential of the conduction (-0.59 V vs. NHE) and valence (+1.48 V vs. NHE) bands for water splitting.

Bidirectional rectifier with gate voltage control based on Bi2O2Se/WSe2 heterojunction

Two-dimensional (2D) WSe2 has received increasing attention due to its unique optical properties and bipolar behavior. Several WSe2-based heterojunctions exhibit bidirectional rectification characteristics, but most devices have a lower rectification ratio. In this work, the Bi2O2Se/WSe2 heterojunction prepared by us has a type Ⅱ band alignment, which can vastly suppress the channel current through the interface barrier so that the Bi2O2Se/WSe2 heterojunction device has a large rectification ratio of about 105. Meanwhile, under different gate voltage modulation, the current on/off ratio of the device changes by nearly five orders of magnitude, and the maximum current on/off ratio is expected to be achieved 106. The photocurrent measurement reveals the behavior of recombination and space charge confinement, further verifying the bidirectional rectification behavior of heterojunctions, and it also exhibits excellent performance in light response. In the future, Bi2O2Se/WSe2 heterojunction field-effect transistors have great potential to reduce the volume of integrated circuits as a bidirectional controlled switching device.

Defect engineered N-doped black-V2O5 nanostructures for hydrogen production via solar-catalytic water splitting in the presence of different sacrificial agents

In this study, vanadium pentoxide (V2O5) is synthesized via hydrothermal method and annealed in a normal and NH3 gas ambience, which led to the formation of pristine and defective-V2O5 systems, respectively. This defective-V2O5 contained both doped-nitrogen and oxygen-vacancies defects, confirmed through XRD and XPS analysis. Interestingly, this process also led to the exfoliation of V2O5 into a 2D layered structure, confirmed by FESEM analysis. A band gap energy of ∼2.11 and 2.26 eV is estimated for the defective and pristine-V2O5, respectively from the Tauc's plots. The solar-catalytic green H2 production efficiency (in mmol g−1 h−1) of the pristine and defective-V2O5 in presence of different sacrificial is investigated and estimated, and it is found to the order of glycerol (2.369) > methanol (1.969) > triethanolamine (1.441) > sodium sulphate/sodium sulfide mixture (1.210) > ethylene glycol (0.967). While accounting the inherent properties of the various sacrificial agents, the observed enhanced efficiency of defective-V2O5 is attributed to their surface-active sites, suitable band structure along with the modulations in the charge carrier separation and transfer characteristics of the system, confirmed through BET, PL, Mott–Schottky, electrochemical impedance, and photocurrent measurements. Further, the cyclic photocatalytic efficiency of defective-V2O5 is found to be consistent in all the 3 cycles in a total period of 9 h. The post-characterizations of the recycled defective-V2O5 system suggested that the developed photocatalyst is stable in terms of its photo-chemical and physical properties, suitable for scale up green H2 productions.

Effect of Adhesion Layer at the Pt/TiO2 Interface on the Degradation Pathways of TiO2-Protected III-V Water-Splitting Photocathodes

Photoelectrochemical (PEC) water splitting has been identified as a promising route towards the production of green hydrogen as a solar fuel to meet the global energy demands [1]. Highly efficient photoelectrodes made of III-V compounds are promising candidates to reach the goal of >15% solar-to-hydrogen efficiency [2]. However, the main bottle neck of these materials is their poor stability in direct contact with acidic electrolytes, which is needed to ensure efficient mass transport and an efficient hydrogen evolution reaction (HER). Atomic layer deposited (ALD) titanium dioxide (TiO2) is commonly utilized as a protective layer to shield the absorber from the electrolyte [3]. To reduce HER overpotentials, the TiO2 film needs to be modified with a catalyst layer. In a demonstration of a TiO2 protected III-V PEC device, Cheng et al. proposed that the detachment of the catalyst layer induced the degradation of the protective TiO2 film in a pH 0 electrolyte which eventually led to the corrosion of the photoabsorber [4].In this work, GaInP/GaAs/Ge photocathodes for water reduction were protected with ALD TiO2 layers deposited from tetrakis(dimethylamido)titanium (TDMAT) and water precursors with varying thicknesses. A 2 nm catalytic Pt layer was deposited via electron beam evaporation (EBE) to reduce the overpotential of the HER. The conformal coverage of the absorber with TiO2 was confirmed with atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). None of the TiO2 films were able to stabilize the illuminated III-V electrodes for 60 min at 0 V versus the counter electrode (CE) in a pH 0 electrolyte (1 M H2SO4). Characterization of the electrochemical potential at the electrode’s front side revealed an unstable regime for the TiO2 protection layer. ICP-MS of the electrolytes, SEM/EDX and electrochemical analyses revealed the detachment of the catalytic Pt layer that led to the dissolution of the TiO2 and the III-V degradation (Figure 1A). The adhesion of Pt on TiO2 was improved by depositing a 2 nm Ti layer via EBE at the Pt/TiO2 interface (Figure 1B). The adhesion layer acts as a wetting layer for Pt, reducing the nucleation energy barrier and increasing the number of nucleation sites compared to Pt/TiO2. The enhanced wetting is due to the formation of Ti−Pt chemical bonds [5] and the overpotential @ 10 mA/cm2 to perform HER was 60 mV, similar to that of a pristine EBE Pt layer. The Ti layer greatly improves the stability of TiO2/III-V photoelectrodes, confirming the results of Cheng et al. and illustrating the importance of a stable catalyst layer.Figure 1. A) SEM micrograph of degradation of Ge/GaAs/GaInP/TiO2/Pt photocathode after 60 min. of photocurrent measurements at 0 V vs. CE in 1 M H2SO4. B) Accelerated stability test in dark for 2 nm Pt/15 nm TiO2 on FTO with (red curve) and without (black curve) a 2 nm Ti adhesion layer in between the Pt and TiO2 layers.

Charge Carrier Trapping in the Surface Region of BiVO4 Photoanodes

Photoelectrochemical water splitting is a promising method for converting solar energy into chemical energy stored in molecular hydrogen and oxygen. However, the efficiency of this process is heavily dependent on the properties of the photoelectrode materials used. Metal oxide semiconductors, such as BiVO4, are commonly used as photoanode materials, but they have poor charge transport properties and surface catalytic activity, which can limit their efficiency.To address these limitations, catalysts are often incorporated onto the surface of the photoanode to improve its surface activity. However, the overall efficiency of the photoelectrochemical process is also influenced by charged defect sites present both in the bulk and on the surface of the semiconductor. These defect sites can trap charges and hamper the kinetics of the process in the millisecond time scale. To address this issue, covalently coordinated catalyst layers and surface doping can be used to eliminate these trapped charges. Moreover, the bulk charge carriers are not entirely decoupled from the surface processes and can be influenced by surface treatments. Therefore, a multi-folded approach that considers both the surface and bulk properties of the photoanode, as well as the role of the catalysts, is necessary to improve the overall efficiency of photoelectrochemical water splitting.We have investigated interfacial charge trapping and transfer processes through a CoOx catalyst layer deposited on BiVO4 by atomic layer deposition (ALD) and cobalt incorporated into the subsurface region. We have shown, by the combination of activity studies and spectroscopy investigations, that oxygen vacancies modified by cobalt incorporation have a remarkable impact on the water oxidation activity and charge injection efficiency. We further demonstrated by transient photocurrent measurements performed by fast LED light pulses (within ms time scale) that the CoOx catalyst layer reduced the number of trapped electrons and improved the rate of charge utilization. Cobalt ions in the subsurface region on the other did not act as catalytic centers but they eliminated the trapping process. We have also confirmed these observations by transient absorption spectroscopy investigations and showed that cobalt incorporation had a much bigger effect on the charge recombination lifetime.

Synergy Effect of Plasmonic Field Enhancement and Light Confinement in Mesoporous Titania-Coated Aluminum Nanovoid Photoelectrode.

Photoelectrochemical (PEC) water splitting is a highly demanded technology for the realization of sustainable society. Various types of photoanodes have been developed to achieve high efficiency of PEC water splitting. Plasmonic field enhancement and light confinement effects are often adopted to improve PEC performance. However, their synergistic effects have not been studied. In this work, a mesoporous TiO2 layer was deposited on an Al plate with a nanovoid array structure, which acts as a photoanode and simultaneously exhibits a light confinement effect and surface plasmon resonance. The solo and synergy effects were investigated through experimental photocurrent measurements and theoretical simulations using the finite-difference time-domain method. The highest improvement in PEC performance was confirmed when the synergy effect occurred.

Facile in-situ synthesis of solid mediator based CdS-rGO-WO3 Z-scheme photocatalytic system for efficient photocatalytic hydrogen generation

Reduced graphene oxide (rGO) solid state mediator based Z scheme photocatalyst CdS-rGO-WO3 heterojunction comprising of nano-rods of CdS and nanoplates of WO3 was fabricated in-situ by a facile hydrothermal process, characterized and tested for solar hydrogen generation. The systematically designed heterojunction created separated oxidative and reductive sites for photo generated electron hole pairs with enhanced redox ability, improving the charge separation and photo-stability, mitigating the problem of photo-corrosion of CdS. This was evident from an enhanced photocatalytic activity of 11.69 mmolg−1h−1 which was almost 2.3 times than pristine CdS (4.9 mmolg−1h−1), in presence of simulated solar light. Due to the high electron mobility property of graphene sheet, rapid transport of electrons was possible at the interface between CdS and WO3. The charge transfer via Z scheme mechanistic pathway was verified by X-ray Photoelectron Spectroscopy (XPS), Photoluminescence (PL) and photocurrent measurement studies. This research study will provide a newer insight in engineering nano-hetero-structures for enhanced photocatalytic hydrogen evolution, in an attempt to make the process commercially viable.

Understanding the reaction mechanism and kinetics of photocatalytic oxygen evolution on CoOx-loaded bismuth vanadate.

Photocatalytic water splitting for green hydrogen production is hindered by the sluggish kinetics of oxygen evolution reaction (OER). Loading a co-catalyst is essential for accelerating the kinetics, but the detailed reaction mechanism and role of the co-catalyst are still obscure. Here, we focus on cobalt oxide (CoOx) loaded on bismuth vanadate (BiVO4) to investigate the impact of CoOx on the OER mechanism. We employ photoelectrochemical impedance spectroscopy and simultaneous measurements of photoinduced absorption and photocurrent. The reduction of V5+ in BiVO4 promotes the formation of a surface state on CoOx that plays a crucial role in the OER. The third-order reaction rate with respect to photohole charge density indicates that reaction intermediate species accumulate in the surface state through a three-electron oxidation process prior to the rate-determining step. Increasing the excitation light intensity onto the CoOx-loaded anode improves the photoconversion efficiency significantly, suggesting that the OER reaction at dual sites in an amorphous CoOx(OH)y layer dominates over single sites. Therefore, CoOx is directly involved in the OER by providing effective reaction sites, stabilizing reaction intermediates, and improving the charge transfer rate. These insights help advance our understanding of co-catalyst-assisted OER to achieve efficient water splitting.

Fabrication of BiVO4 photoanode loaded with Zn-doped Co9S8 for enhanced photoelectrochemical performance

The Zn-Co9S8/BiVO4 composite photoanodes were fabricated by loading Zn-doped Co9S8 nanoparticles to the electrodeposited BiVO4 photoelectrode. The composite photoanodes showed enhanced photoelectrocatalytic performance for the degradation of tetracycline. The improved separation of photogenerated carriers were evidenced by photocurrent measurement, electrochemical impedance spectroscopy, photoluminescence spectroscopy, and applied bias photon-to-current efficiency. Electron spin resonance spectroscopy and free radical scavenging experiments confirmed that OH, h+ andO2− played dominant roles. The optimized Zn-Co9S8/BiVO4 composite photoanode showed 2.5 times higher photocurrent density than BiVO4 photoanode. The Zn-Co9S8/BiVO4 photoanode presented an incident photon-to-current conversion efficiency of 56 %, higher than BiVO4 (25 %). According to the density functional theory results, a heterojunction between Zn-Co9S8 to BiVO4 was formed, prompting the separation of photogenerated pairs. The Zn-Co9S8/BiVO4 photoanode maintained good photoelectrocatalytic activity after five reuse cycles, confirming its good stability.

Gate-controlled suppression of light-driven proton transport through graphene electrodes

Recent experiments demonstrated that proton transport through graphene electrodes can be accelerated by over an order of magnitude with low intensity illumination. Here we show that this photo-effect can be suppressed for a tuneable fraction of the infra-red spectrum by applying a voltage bias. Using photocurrent measurements and Raman spectroscopy, we show that such fraction can be selected by tuning the Fermi energy of electrons in graphene with a bias, a phenomenon controlled by Pauli blocking of photo-excited electrons. These findings demonstrate a dependence between graphene’s electronic and proton transport properties and provide fundamental insights into molecularly thin electrode-electrolyte interfaces and their interaction with light.