Photoelectrochemical Investigations Research Articles

Acceleration of bulk and surface charger transfer dynamics via FePi cocatalyst-coated Ti/(Sb)-Fe2O3:Sb/(Ti)-Fe2O3 type-II homojunction photoanode for photoelectrochemical performance

Hematite (α-Fe2O3) possesses notable benefits in the field of photoelectrochemical (PEC) water splitting. However, the overall low efficiency of the separation and transfer of photogenerated charge carriers significantly hinders its further utilization. Although the occurrence of an internal electric field has the potential to significantly augment the efficiency of charge separation and transfer, there is a crucial need to broaden the scope of its successful application. This study explores a strategy for modifying the coupling between homojunction formation with gradient doping and cocatalyst modification on hematite to boost PEC performance. The developed type II Ti-doped/(Sb-codoped) Fe2O3:Sb-doped/(Ti-codoped) Fe2O3 (Ti/(Sb)-HT:Sb/(Ti)-HT) homojunction with a staggered band alignment accelerated the bulk charge separation via an intrinsic built-in electric field, while the bulk conductivity was improved using a gradient co-doping approach. Furthermore, the deposition of a FePi cocatalyst expedited the transfer of holes from the photoanode to the electrolyte by increasing the surface states, thereby hastening the water oxidation kinetics. The resulting Ti/(Sb)-HT:Sb/(Ti)-HT@FePi photoanode exhibited a 78.7% increase in photocurrent density compared to the bare Ti-Fe2O3 photoanode (0.94–1.68 mA/cm2 at 1.23 VRHE), accompanied by a charge transfer efficiency of 72.5%. Comprehensive photoelectrochemical investigations revealed that the homojunction and cocatalyst play a vital role in improving the dynamics of both the bulk and surface of the hematite photoanode, thereby facilitating efficient water oxidation. These findings offer a deeper insight into the function of homojunction photoanodes adorned with cocatalysts in the solar water-splitting process.

Photoelectrochemical investigations of cadmium sulfide-doped silver (CdS) on flexible substrates

Photoelectrochemical investigations of cadmium sulfide-doped silver (CdS) on flexible substrates

CdS-Based Hydrothermal Photocatalysts for Complete Reductive Dehalogenation of a Chlorinated Propionic Acid in Water by Visible Light.

Cadmium sulfide (CdS)-based photocatalysts are prepared following a hydrothermal procedure (with CdCl2 and thiourea as precursors). The HydroThermal material annealed (CdS-HTa) is crystalline with a band gap of 2.31 eV. Photoelectrochemical investigation indicates a very reducing photo-potential of -0.9 V, which is very similar to that of commercial CdS. CdS-HTa, albeit having similar reducing properties, is more active than commercial CdS in the reductive dehalogenation of 2,2-dichloropropionic acid (dalapon) to propionic acid. Spectroscopic, electro-, and photoelectrochemical investigation show that photocatalytic properties of CdS are correlated to its electronic structure. The reductive dehalogenation of dalapon has a double significance: on one hand, it represents a demanding reductive process for a photocatalyst, and on the other hand, it has a peculiar interest in water treatment because dalapon can be considered a representative molecule of persistent organic pollutants and is one of the most important disinfection by products, whose removal from the water is the final obstacle to its complete reuse. HPLC-MS investigation points out that complete disappearance of dalapon passes through 2-monochloropropionic acid and leads to propionic acid as the final product. CdS-HTa requires very mild working conditions (room temperature, atmospheric pressure, natural pH), and it is stable and recyclable without significant loss of activity.

Ag-decorated flower-like WSe2 for enhanced photocatalytic CO2 reduction

In this work, flower-like Ag/WSe2 was synthesized through solvothermal method and in situ photodeposition. Ag nanoparticles were uniformly dispersed and the catalyst exhibited a much better CO yield rate of 14.80 µmol g–1h−1 as compared with that of WSe2 (5.24 µmol g–1h−1). Based on photoelectrochemical investigation, this was mainly attributed to the enhancement of visible light absorption along with improved charge separation and transfer at the interface of Ag/WSe2.

Photoelectrochemical Properties and Characterization of CdS/CdSe Heterojunctions Obtained by CBD on ITO and p–Si Substrates

AbstractThis research investigates the optical, structural, electrical, and photoelectrochemical characteristics of CdS/CdSe heterojunctions formed on both ITO and p–Si substrates. The deposition of CdS and CdSe films was carried out using the chemical bath deposition method, which is economical and simple method. The optical, structural, and electrical properties of CdS/CdSe heterojunctions were analyzed through UV–Vis spectrometry, photoluminescence (PL) spectroscopy, field emission–scanning electron microscopy (FE‐SEM), X‐ray diffraction (XRD), Raman spectroscopy, and Hall‐effect measurements. Furthermore, Mott–Schottky analysis was employed to investigate the electrochemical properties of the semiconductor CdS/CdSe heterojunctions on both ITO and p–Si substrates. Additionally, the photoelectrochemical investigations of CdS/CdSe heterojunctions on ITO and p–Si substrates were conducted by electrochemical analyses using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and photocurrent – time plots under both dark and illuminated conditions.

UV‐to‐NIR Harvesting Conjugated Porous Polymer Nanocomposite: Upconversion and Plasmon Expedited Thioether Photooxidation

AbstractPhotocatalysts capable of harvesting a broad range of the solar spectrum are essential for sustainable chemical transformations and environmental remediation. Herein, we have integrated NIR‐absorbing upconversion nanoparticles (UCNP) with UV‐Vis absorbing conjugated porous organic polymer (POP) through the in situ multicomponent C−C coupling to fabricate a UC−POP nanocomposite. The light‐harvesting ability of UC−POP is further augmented by loading plasmonic gold nanoparticles (AuNP) into UC−POP. A three‐times enhancement in the upconversion luminescence is observed upon the incorporation of AuNP in UC−POP, subsequently boosting the photocatalytic activity of UC−POP−Au. The spectroscopic and photoelectrochemical investigations infer the enhanced photocatalytic oxidation of thioethers, including mustard gas simulant by UC−POP−Au compared to POP and UC−POP due to the facile electron‐hole pair generation, suppressed exciton recombination, and efficient charge carrier migration. Thus, the unique design strategy of combining plasmonic and upconversion nanoparticles with a conjugated porous organic polymer opens up new vistas towards artificial light harvesting.

UV-to-NIR Harvesting Conjugated Porous Polymer Nanocomposite: Upconversion and Plasmon Expedited Thioether Photooxidation.

Photocatalysts capable of harvesting a broad range of the solar spectrum are essential for sustainable chemical transformations and environmental remediation. Herein, we have integrated NIR-absorbing upconversion nanoparticles (UCNP) with UV-Vis absorbing conjugated porous organic polymer (POP) through the in situ multicomponent C-C coupling to fabricate a UC-POP nanocomposite. The light-harvesting ability of UC-POP is further augmented by loading plasmonic gold nanoparticles (AuNP) into UC-POP. A three-times enhancement in the upconversion luminescence is observed upon the incorporation of AuNP in UC-POP, subsequently boosting the photocatalytic activity of UC-POP-Au. The spectroscopic and photoelectrochemical investigations infer the enhanced photocatalytic oxidation of thioethers, including mustard gas simulant by UC-POP-Au compared to POP and UC-POP due to the facile electron-hole pair generation, suppressed exciton recombination, and efficient charge carrier migration. Thus, the unique design strategy of combining plasmonic and upconversion nanoparticles with a conjugated porous organic polymer opens up new vistas towards artificial light harvesting.

Bismuth Vanadate and 3D Graphene Composite Photoanodes for Enhanced Photoelectrochemical Oxidation of Water.

Bismuth vanadate (BiVO4) has been one of the most promising photoanodes for the photoelectrochemical (PEC) water oxidation process. Efforts are still on to overcome the drawbacks of this photoanode to enhance the catalytic efficiency and improve the stability. In the present work, three-dimensional graphene (3D-G) was incorporated inside the BiVO4 matrix, primarily to improve the conductivity of the material. The photoanodes are fabricated with the incorporation of a SnO2 heterojunction and application of cobalt borate (Co-Bi) as a cocatalyst. The incorporation of 3D-G has enhanced the photocurrent from 0.72 o 1.21 mA cm-2 in ITO/SnO2/BiVO4 and ITO/SnO2/3D-G-BiVO4 materials; the photocurrent has been improved from 0.89 to 1.52 mA cm-2 in ITO/SnO2/BiVO4/Co-Bi and ITO/SnO2/3D-G-BiVO4. Semiconductor properties are evaluated from the Mott-Schottky measurements, and the charge transfer and transport kinetics of the PEC process are measured from several photoelectrochemical investigations. Both the charge transport and the charge transfer efficiencies are enhanced upon inclusion of 3D-G into the catalyst system. The lifetime of the charge carrier is observed to be increased. The decrease in the decay kinetics of the holes, enhancement in the open-circuit photovoltage (OCPV), and the resulting modulation of the surface states are responsible for the enhancement in the surface charge transfer process due to the inclusion of 3D-G into the catalytic system. Therefore, the additional role of 3D-G in the modulation of the surface states and release of the Fermi level pinning has made the band alignment between the semiconductor and the analyte better, which resulted in enhanced catalytic performance in the photoelectrochemical oxidation of water.

Symbiotic MoO3-SrTiO3 Heterostructured Nanocatalysts for Sustainable Hydrogen Energy: Combined Experimental and Theoretical Simulations.

Highly efficient Z-scheme MoO3-SrTiO3 heterostructured nanocatalytic systems were engineered via a sol-gel chemical route and exploited in green H2 energy synthesis via overall water splitting. The optical and electronic investigations corroborated the enhancement of the optoelectronic properties of SrTiO3 after the incorporation of MoO3. Emergence of the interfacial charge transfer between SrTiO3 and MoO3 is the driving force, which synergistically triggered the catalytic efficiency of MoO3-SrTiO3 heterostructures. The substitution of Ti4+ by Mo6+ ions led to the suppression of Ti3+ mid-gap states, as the potential involved in the Mo6+/Mo5+ reduction is higher than that in Ti4+/Ti3+. Theoretical studies were employed in order to comprehend the mechanism behind the advancement in the catalytic activity of MoO3-SrTiO3 porous heterostructures, which also possessed a higher surface area. 2% MoO3-SrTiO3 exhibited the optimum catalytic response toward H2 evolution via photochemical, electrochemical, and photo-electrochemical water splitting. 2% MoO3-SrTiO3 evolved H2 at the fourfold higher rate than SrTiO3 with phenomenal 16.06% AQY during photochemical water splitting and photo-degraded MB dye at nearly 88% against the 42% degradation in SrTiO3-led photocatalysis. Electrochemical and photo-electrochemical investigations also manifested the superiority of 2% MoO3-SrTiO3 toward HER, as it exhibited accelerated current and photocurrent densities of 25.02 and 27.45 mA/cm2, respectively, at the 1 V potential. EIS studies demonstrated the improved charge separation efficiency of MoO3-SrTiO3 heterostructures. This work highlights the multi-dimensional approach of obtaining green H2 energy as the sustainable energy source using MoO3@SrTiO3 heterostructures.

A measurement system for photoelectrochemical processes with high‐quality irradiation, temperature control, and automated gas analysis

AbstractIn this Application Note, a versatile and reliable measurement system for photoelectrochemical investigations is described which aims to assist scientists in obtaining reproducible photoelectrochemical data of high quality, including the solar‐to‐hydrogen (STH) efficiency. Specifically, it addresses the parameters irradiation quality, reaction temperature, and gas measurement. The setup is designed to exclude stray light and uses a solar‐grade mirror to reflect the light of a vertical solar simulator on the electrochemical cell. The light quality in the setup (»AAA«, IEC 60904‐9) is close to the classification of the solar simulator itself. The temperature in the electrochemical cell is controlled with an external Peltier element and can be kept constant in the range of 20–45°C. The influence of reaction temperature on the photocurrent of a WO3 photoanode is demonstrated. The gaseous reaction products are analyzed with a mobile gas chromatograph, using an automated measurement routine with discontinuous sampling from the electrochemical cell. The system is applied to determine the Faraday and STH efficiencies of a copper indium gallium selenide photocathode.

ZIF-67 templated Co2+, cyanate-doping to construct S-schemed carbon nitride junction for boosting photocatalytic H2 evolution

Herein a novel carbon nitride (CN) homojunction between Co2+, cyanate group spatially co-doped and undoped domain is first designed via the ZIF-67 self-templated doping and polymeric condensation of CN, for efficient photocatalytic H2 evolution (PHE). The microstructure characterizations on the ZIF-67 amount-dependent crystallinity and modifications confirm the successful construction of CN homojunction between Co2+-concentrated domain and undoped domain (CoCN). As a result, the optimized CoCN shows an improved PHE rate (2512 μmol·g−1·h−1) 2.93 times that of pristine CN, with further 1.7 times increase after 5 rounds of cycling (4305 μmol·g−1·h−1). Steady-transient photoluminescence and photo-electrochemical investigations demonstrate that ZIF-67 self-templated doping enhances visible light absorption and the separation/transfer of photogenerated carriers. Further energy-band analysis suggests that the coupling of the doped and undoped domains facilitates the built-in electric field and band bending, leading to Self-S-Scheme mechanism of photocatalysis. This work provides a new method for the design of CN-based junctions via ZIF-67 templated doping boosting photocatalytic activity.

Evaluation of local oxygen flux produced by photoelectrochemical hydroxide oxidation by scanning electrochemical microscopy

Several in-situ electrochemical approaches have been developed for performing a localized photoelectrochemical investigation of the photoanode. One of the techniques is scanning electrochemical microscopy (SECM), which probes local heterogeneous reaction kinetics and fluxes of generated species. In traditional SECM analysis of photocatalysts, evaluation of the influence of radiation on the rate of studied reaction requires an additional dark background experiment. Here, using SECM and an inverted optical microscope, we demonstrate the determination of O2 flux caused by light-driven photoelectrocatalytic water splitting. Photocatalytic signal and dark background are recorded in a single SECM image. We used an indium tin oxide electrode modified with hematite (α-Fe2O3) by electrodeposition as a model sample. The light-driven flux of oxygen is calculated by analysis of SECM image recorded in substrate generation/tip collection mode. In photoelectrochemistry, the qualitative and quantitative knowledge of oxygen evolution will open new doors for understanding the local effects of dopants and hole scavengers in a straightforward and conventional manner.

Structural and Optical Characterization of Electrochemically Deposited Indium Oxide Nanostructures for Photoelectrochemical Investigation

Herein, we studied the effect of different precursor solution pH values on the crystal structure, morphology, and optical properties of high-purity In2O3 nanostructures for their possible photoelectrochemical application via the electrodeposition technique. The XRD result revealed predominant growth in the (222) plane with the highest intensity for the sample of pH 4; the grain sizes decreased with rising pH in the range from 28.03 to 36.89 nm, having the minimal value at pH 4. The micrographs showed highly crystalline nanostructures, with the densest morphology at pH 4, which was attributed to the lowering of the film growth rate as the pH rises. The energy band gap demonstrated a slight shrinkage with increasing pH in the range of 2.86–2.93 eV and the reflectance was dominant in the visible and near-infrared regions, with relatively low values for all of the film samples, showing a minimal value at pH 4, thus confirming it to be the optimal pH for a most suitable In2O3 electrode for photoelectrochemical application. The I–V properties measured under 100 W simulated illumination showed an enhanced photocurrent, which increases with rising pH in the range of 0.134–0.188 mA/cm2, making a peak with the electrode of pH 4. The electrochemical impedance spectra (EIS) of In2O3 were in firm agreement with earlier results. Overall, these results suggest that pH 4 is the optimum pH to obtain the best-quality In2O3 nanostructure for PEC application.

Structural and photoelectrochemical investigation of pulse electrodeposited AgIn0.9Ga0.1S2 thin films

Structural and photoelectrochemical investigation of pulse electrodeposited AgIn0.9Ga0.1S2 thin films

Morphologically Tunable Fabrication of Hematite Nanostructures for Enhanced Photoelectrochemical Performance

Herein, a photoelectrochemical investigation of photoanodes based on hematite nanorods and nanospheres fabricated via hydrothermal technique is reported. The fabricated nanostructures have been thoroughly analyzed and characterized using field emission scanning electron microscopy (FESEM), X-ray Diffractometer (XRD), UV-Visible spectroscopy, Photoluminescence spectroscopy (PL), and X-ray photoelectron spectroscopy (XPS). The presence of oxygen vacancies and morphological characteristics of Hematite photoanodes were shown to be directly related to their photoelectrochemical performances. The nanorod-based photoanode yields an excellent photocurrent density of 1.63 mAcm2 which was about 4 times greater than the nanosphere-based photoanode. Further hematite nanorods showed efficient charge transfer kinetics, increased donor density and, excellent photo stability. The enhancement in photoelectrochemical properties of nanorods can be attributed to the oxygen vacancies generated in hematite nanorods which provide excellent electrical conductivity and better charge transfer kinetics. The results demonstrate that oxygen vacancy-rich nanorods can serve as ideal photoelectrode for enhancing the electrochemical properties of hematite nanostructures.

Hollow bi-Janus hetero-nanofibers as a bi-functional photoreforming catalyst for prominently boosting hydrogen evolution from water-pollutant system

Bi-functional photoreforming catalysts are promising for synergetic hydrogen evolution and pollutant removal through a water-pollutant system. The rational energy band and interface engineering are crucial in promoting their performance but are still challenging due to finely regulating nanoscale interface difficulties. Herein, single to bi-Janus interface engineering is adopted to develop hollow bi-Janus SrTiO3/ZnO/TiO2 hetero-nanofibers with gradient energy band and spatially separated redox surfaces via electrospinning married atomic layer deposition methods. The simulations indicate that these novel structures have a stronger internal electric field (5.72 ×106 V/m) than SrTiO3/ZnO (1.84 ×106 V/m) and ZnO/TiO2 (3.98 ×106 V/m) single-Janus hetero-nanofibers (SJ-HNFs), and more ordered electric field distribution than mixed hetero-nanofibers (MHNFs). Experimentally, they have better charge separation and directional carriers transfer path, as evidenced by photoluminescence, photovoltage, and photoelectrochemical investigations, along with photo-deposition probe experiments. The gradient energy band, directional charge transfer path, and spatially separated redox surfaces promote their photoreforming performance effectively, presenting a high photoreforming hydrogen evolution rate of 104.6 μmol g−1 h−1 in 10,000 ppm propranolol (corresponding degradation of 33.1% after 5 h), about 3.62, 4.27, and 3.11 times of ZnO/TiO2 SJ-HNFs, SrTiO3/ZnO SJ-HNFs and SrTiO3/ZnO/TiO2 MHNFs. This work provides a promising interfacial engineering strategy for designing photoreforming catalyst to simultaneously achieve energy conversion and environmental pollution treatment.

Enhanced photocatalytic and photoelectrochemical investigation of Ce and Eu modified titanium nanotube arrays towards dye removal

ABSTRACT Cerium and europium-doped titanium nanotube (Ce and Eu-TNTs) were obtained by one-step electrochemical anodization. SEM micrographs show highly ordered nanotubes for pure- TNTs but less organized and more spaced nanotubes for Ce and Eu-TNTs. The XRD results show that anatase is the dominant phase, and the doping does not change the crystalline phase. EIS plots indicated that Ce/Eu doped TNTs photocatalysts possesses a lower electron transfer resistance than pure TNTs, which is related to an effective separation of photogenerated electron/hole pairs. The photodegradation results showed that Ce-TNTs (0.5 mM) and Eu-TNTs (2 mM) photocatalysts exhibit the best enhancement of AB removal reaching a reaction rate of (kapp = 0.026 min−1, t1/2 = 19 min) and (kapp = 0.020 min−1, t1/2 = 20 min), respectively, under initial pH = 3 and CAB = 10 mg.L−1, compared to (kapp = 0.014 min−1, t1/2 = 35 min) for pure TNTs. The adsorption efficiency carried out in the dark after 30 min is enhanced by Ce and Eu-doping and reaches its maximum to 52.08% for Eu-TNTs (2 mM) compared to only (31.11% and 32.96%), respectively, for Ce-TNTs (0.5 mM) and pure TNTs catalyst.

A novel Ag/g-C3N4/ZnO/Fe3O4 nanohybrid superparamagnetic photocatalyst for efficient degradation of emerging pharmaceutical contaminant (Pantoprazole) from aqueous sources

Owing to their remarkable properties, such as concentration of energetic photons, scattering of photons and demonstration of surface plasmon resonance (SPR), the use of plasmonic noble metals in the construction of a nanohybrid photocatalyst holds great promise of enhancing photodegradation rates. The current work puts forth a facile route of fabrication of a robust Ag/g-C3N4/ZnO/Fe3O4 hybrid, superparamagnetic nano-photocatalyst for express photodegradation of pantoprazole, a prototype of a pharmaceutical. The absorption edge of the nano-scaled hybrid photocatalyst was found to be ~ 2.25 eV suggesting fine-tuning of band edges of its moieties. Photoluminescence studies and photoelectrochemical investigations of the hybrid photocatalyst revealed a diminished rate of electron-hole recombination that further suggested enhanced separation of charge carriers attained through synergistic effects of individual moieties. g-C3N4 and Fe3O4 proved to be of immense consequence vis-à-vis separation of photoinduced charge carriers. Alone the photocatalyst achieved 98.24% disintegration of pantoprazole within 40 min with a stupendous pseudo-first order velocity constant of 0.10231 min−1. The performance of the quaternary photocatalyst was also evaluated in presence of various co-existing substances as well as in environmental water samples.

Multiple Effects Induced by Mo6+ Doping in BiVO4 Photoanodes

Mo6+ doping increases the photoelectrochemical performance of BiVO4 photoanodes in water oxidation. Herein, the underlying mechanisms is elucidated through a systematic structural, morphological, and photoelectrochemical investigation on photoelectrodes of pure and Mo6+ doped BiVO4 prepared by a novel multistep spin‐coating deposition approach, leading to multilayer flat films with high optical transparency. Transient absorption spectroscopy in the nano‐ to microsecond time scale reveals a longer lifetime of photogenerated holes in the doped films. Besides confirming that Mo6+ ions improve the electron transport in the material bulk, impedance spectroscopy also reveals the crucial role of the dopant on the surface properties of BiVO4 photoanodes. The presence of intra‐bandgap states, acting as traps of photogenerated charge carriers in pure BiVO4, is detected through the build‐up of the interfacial surface state capacitance. The limited activity of pure BiVO4 in water oxidation is largely improved upon 3 at% Mo6+ incorporation, ensuring a more efficient charge carrier transport with respect to pure BiVO4, together with the beneficial passivation of its trap surface states.

Visible Light Reductive Photocatalysis of Azo-Dyes with n-n Junctions Based on Chemically Deposited CdS.

New composite photocatalysts have been obtained by chemical bath deposition of CdS on top of either nanostructured crystalline ZrO2 or TiO2 films previously deposited on conductive glass FTO. Their morphological, photoelectrochemical and photochemical properties have been investigated and compared. Time resolved spectroscopic, techniques show that in FTO/TiO2/CdS films the radiative recombination of charges, separated by visible illumination of CdS, is faster than in FTO/ZrO2/CdS, evidencing that carrier dynamics in the two systems is different. Photoelectrochemical investigation evidence a suppression of electron collection in ZrO2/CdS network, whereas electron injection from CdS to TiO2 is very efficient since trap states of TiO2 act as a reservoir for long lived electrons storage. This ability of FTO/TiO2/CdS films is used in the reductive cleavage of N=N bonds of some azo-dyes by visible light irradiation, with formation and accumulation of reduced aminic intermediates, identified by ESI-MS analysis. Needed protons are provided by sodium formate, a good hole scavenger that leaves no residue upon oxidation. FTO/TiO2/CdS has an approximately 100 meV driving force larger than FTO/ZrO2/CdS under illumination for azo-dye reduction and it is always about 10% more active than the seconds. The films showed very high stability and recyclability, ease of handling and recovering.