Modulation of Lewis and Brønsted Acidic Sites to Enhance the Redox Ability of Nb2O5 Photoanodes for Efficient Photoelectrochemical Performance

Construction of a heterojunction between Ni/Al layered double oxides and CdS quantum dots for efficient photocatalytic hydrogen production

The Ni/Al layered double oxide (Ni/Al-LDO) is a promising photocatalyst because of the high surface area and abundant active sites. However, the application of Ni/Al-LDO for photocatalytic hydrogen evolution is hindered by the unclarity of the optimized microstructure and limited light absorption. In this work we report the structural evolution from Ni/Al layered double hydroxides (Ni/Al-LDH) to Ni/Al-LDO, which is able to achieve a precise regulation of the layered structure with abundant acid sites for photocatalysis. Further, CdS quantum dots (QDs) are in-situ grown on the sheet-like Ni/Al-LDO to obtain a close contact 0D/2D CdS-Ni/Al-LDO heterojunction. CdS-Ni/Al-LDO exhibits a hydrogen evolution efficiency of 20.3 mmol/g/h and an apparent quantum yield (AQY) of 22.2 % at a wavelength of 450 nm. The superior performance is attributed to the synergistic effects of abundant Lewis and Brønsted acid sites of Ni/Al-LDO, the layered structure with a high specific surface area and the heterojunction between Ni/Al-LDO and the CdS QDs.

d-Orbital Single Electron Filling O─O π* Bonds on WO3S1 Sites for Highly Selective Generation of Hydroxyl Radicals

Hydroxyl radical (•OH) stemming from dissolved oxygen (O2) via photocatalysis is very attractive, but its poor selectivity and generation efficiency greatly limit its application. Herein, a kind of tungsten single site co-coordinated with O and S atoms (WO3S1) is established on ZnIn2S4 (W-ZIS). The strong interactions in WO3S1 shift the d-band center toward the Fermi level, enhancing the adsorption of O2. These interactions improve the accumulation of photo-generated electrons on WO3S1, facilitating the dissociation of O─O bonds in crucial intermediates and promoting the selective conversion from O2 into •OH. This brings a state-of-the-art selectivity (40.2%) and generation efficiency (1668.90 mmol. g-1. L-1. h-1) of •OH production. Experimental results and theoretical simulations have elucidated that O2 can be reduced by d-orbitals single electron (↑, _, _, _, _, _) of WO3S1 transfer to 2p-orbital O─O pi anti-bonding (π*: px and py), initially activating O2. Additionally, WO3S1 sites facilitate the cleavage of H2O, optimizing proton adsorption through W─O orbital coupling in WO3S1 and promoting the transformation of oxygen-containing intermediates. More importantly, d-orbitals single electron can fill O─O π* bond in •OOH intermediate, weakening the covalency of the O─O bond, mitigating the formation of H2O2 and shortening the pathway for •OH generation.).

Long-Term Selective Photoelectrochemical Glycerol Oxidation via Oxygen Vacancy Modulated Tungsten Oxide with Self-Healing

The photoelectrochemical selective oxidation of biowaste glycerol into the high value-added material, along with hydrogen production, holds significant promise for advancing renewable and sustainable energy technologies. Here, the surface oxygen state of tungsten oxide is modified to selectively oxidize glycerol into glyceraldehyde, a high-value-added material, and the selectivity is maintained over a prolonged period using the photo-stimulated self-recovery capability. The surface-coordinated photoelectrode exhibits high charge transfer efficiency to glycerol and favorable glycerol adsorption capacity, enabling the selective conversion of glycerol. At 1.2 VRHE in a 2 m glycerol electrolyte adjusted to pH 2, the tungsten oxide photoelectrode achieves a photocurrent density of 2.58 mA cm-2 and a production rate of 378.8 mmol m-2 h-1 with selectivity of 86.1%. The high selectivity is preserved for 18 h by utilizing the self-healing capability of tungsten oxide to restore initial states modified by photoelectrochemical oxidation. This work sheds light on the design of highly efficient metal oxide photoelectrodes for selective biomass oxidation over extended periods.

SPR Effect Enables Flexible Electronic Environment and Activity of Cd0.7In2.2S4-30 for High-Performance Pyro-PEC Catalytic Capability

Plasma-semiconductor systems hold significant promise in the field of photoelectrocatalysis. In this study, the pyroelectric material cadmium indium sulfide (Cd0.7In2.2S4-30) and Pt were used as catalysts, and a temperature gradient was introduced to investigate the influence of surface plasmon resonance (SPR) effect on the pyroelectric and photocatalytic performance. Interestingly, under the influence of the SPR effect, Cd0.7In2.2S4-30 demonstrates a 1.6-fold and 1.4-fold increase in current density under photocatalytic and pyro-photoelectrocatalytic conditions at 1.23 V vs RHE, respectively. Furthermore, under the protection of surface metal Pt, a notable enhancement in the charge separation efficiency and stability of the photoelectrode material is observed. The combination of outstanding performance reveals that Pt noble metal ions, influenced by the SPR effect, generate a localized electric field at the adjacent semiconductor interface, enhancing the charge transfer capability between metal nanoparticles and the semiconductor, thereby promoting electron-hole separation and improving semiconductor photocatalytic activity. Additionally, the SPR effect increases the yield of high-energy pyro-electrons on plasma metal and facilitates their effective transfer to the semiconductor, thereby promoting the generation of thermally induced electrons. This study reveals the multifaceted of SPR effects on the behaviors of semiconductors and provides an opportunity to rationally design metal-semiconductor photocatalytic materials for efficient solar energy conversion.

Switchable Photoelectric Response in High-Temperature Leadless Molecular Ferroelectric [C4N2H14][BiI5]

Lead-free molecular ferroelectrics have garnered considerable attention for their promising potential, but such species with narrow band gap and sensitive photoelectric response are yet inadequate. Herein, we demonstrated the bulk ferroelectric photovoltaic effect in a novel lead-free molecular ferroelectric [C4N2H14][BiI5] with a Curie temperature (Tc) of 366 K and a narrow band gap (Eg) of 1.92 eV. The transformation of the crystal structure from the polar space group P21 to the nonpolar space group P21/m was elucidated using single-crystal X-ray diffraction. Room-temperature (RT) hysteresis loop reveals the intrinsic ferroelectricity of [C4N2H14][BiI5] with a relative small coercive field (Ec ∼ 0.27 kV/cm), saturation polarization (Ps ∼ 1.87 μC/cm2), and remanent polarization (Pr ∼ 1.61 μC/cm2). [C4N2H14][BiI5]-based solar device exhibits significant PV effects with a steady-state photocurrent (Jsc) of 3.54 μA/cm2 and a photovoltage (Voc) of 0.34 V under AM 1.5 G illumination, which can be significantly improved by adjusting the ferroelectric polarization, reaching a maximum Jsc of 140 μA/cm2 and Voc of 0.51 V. This work offers a promising avenue for lead-free molecular ferroelectric materials in the field of optoelectronic devices.

Aptamer molecular gate functionalized mesoporous SiO2@MB controlled-release system for pollutant detection using Ti(Ⅲ) self-doped TiO2 NTs as active photoanode coupled with electrostatic modulation

Atrazine (ATZ) is a widely used herbicide that can cause serious harm to organisms and ecosystems. An immobilization-free photoelectrochemical (PEC) aptasensor has been herein developed for ATZ based on aptamer molecular gate functionalized mesoporous SiO2@MB controlled release system. Compared with traditional immobilization-based sensors, immobilization-free sensors (IFSs) avoid the modification of the recognition element on the electrode surface. Mesoporous SiO2 with large surface area and good biocompatibility can be used as nanocontainers to stably encapsulate the signal shuttle molecule methylene blue (MB). The bifunctional aptamer (APT) is used not only as the recognition element for ATZ but also as the signal switch to block or release MB. In the presence of ATZ, the specific recognition between ATZ and APT will cause the detachment of APT from the surface of SiO2, thus the molecular gate will open and release MB. Due to pH modulation, the positively charged MB can reach the surface of the negatively charged Ti(III) self-doped TiO2 NTs (Ti(III)-TiO2 NTs) electrode to act as an electron donor, which increases the photocurrent. The immobilization-free aptasensor has shown ultrasensitive detection of ATZ with a wide linear range from 1.0 pM to 100.0 nM and a low detection limit of 0.1 pM. In addition, the sensor has excellent selectivity, stability and anti-interference ability, and has been used in real water sample analysis successfully. This strategy has provided a new idea for the design of advanced immobilization-free PEC sensors for environmental pollutant detection.

Improved Conductivity and in Situ Formed Heterojunction via Zinc Doping in CuBi2O4 for Photoelectrochemical Water Splitting

As a photocathode with a band gap of about 1.8 eV, copper bismuthate (CuBi2O4) is a promising material for photoelectrochemical (PEC) water splitting. However, weak charge transfer capability and severe carrier recombination suppress the PEC performance of CuBi2O4. In this paper, the conductivity and carriers transport of CuBi2O4 are improved via introducing Zn2+ into the synthesis precursor of CuBi2O4, driving a beneficial 110 mV positive shift of onset potential in photocurrent. Detailed investigations demonstrate that the introduction of an appropriate amount of zinc leads to in situ segregation of ZnO which serves as an electron transport channel on the surface of CuBi2O4, forming heterojunctions. The synergistic effect of heterojunctions and doping simultaneously promotes the charge transfer and the carrier concentration. OCP experiment proves that ZnO/Zn-CuBi2O4 possesses better charge separation; the Mott-Schottky curve shows that the doping of Zn significantly enhances the carrier concentration; carrier lifetime calculated from time-resolved photoluminescence confirms faster extraction of carriers.

Enhanced Charge Carrier Dynamics on Sb2 Se3 Photocathodes for Efficient Photoelectrochemical Nitrate Reduction to Ammonia

Ammonia (NH3 ) is recognized as a transportable carrier for renewable energy fuels. Photoelectrochemical nitrate reduction reaction (PEC NO3 RR) offers a sustainable solution for nitrate-rich wastewater treatment by directly converting solar energy to ammonia. In this study, we demonstrate the highly selective PEC ammonia production from NO3 RR by constructing a CoCu/TiO2 /Sb2 Se3 photocathode. The constructed CoCu/TiO2 /Sb2 Se3 photocathode achieves an ammonia Faraday efficiency (FE) of 88.01 % at -0.2 VRHE and an ammonia yield as high as 15.91 μmol h-1  cm-2 at -0.3 VRHE with an excellent onset potential of 0.43 VRHE . Dynamics experiments and theoretical calculations have demonstrated that the CoCu/TiO2 /Sb2 Se3 photocathode possesses high light absorption capacity, excellent carrier transfer capability, and high charge separation and transfer efficiencies. The photocathode can effectively adsorb the reactant NO3 - and intermediate, and the CoCu co-catalyst increases the maximum Gibbs free energy difference between NO3 RR and HER. Meanwhile, the Co species enhances the spin density of Cu, and increases the density of states near the Fermi level in pdos, which results in a high PEC NO3 RR activity on CoCu/TiO2 /Sb2 Se3 . This work provides a new avenue for the feasibility of efficient PEC ammonia synthesis from nitrate-rich wastewater.

Piezoelectric polarization induced by dual piezoelectric materials ZnO nanosheets/MoS2 heterostructure for enhancing photoelectrochemical water splitting

Zinc oxide (ZnO) has a broad range of applications in piezo-photoelectrochemical water splitting. However, the narrow light absorption range and high photogenerated carrier recombination efficiency make ZnO somewhat limited in applying piezo-photoelectrochemical water splitting. Heterogeneous structure construction is a superior handle to these two drawbacks. Herein, few-layer molybdenum disulfide (MoS2) nanospheres are compounded on ZnO nanosheets (NSs) to form a dual-piezoelectric-material heterojunction of ZnO NSs/MoS2. The photocurrent density of ZnO NSs/MoS2 reaches 0.68 mA/cm2 at 1.23 V vs. RHE under ultrasonic vibrations. It is 2.4 times higher than that of ZnO NSs under ultrasonic vibrations. The efficient piezo-photoelectrochemical performance is attributed to increased absorption range and polarization field. On the one hand, the narrow band gap of the few-layer MoS2 widens the light absorption range of ZnO. On the other hand, compared to pure ZnO NSs, ZnO NSs/MoS2 has an enhanced polarization field under ultrasonic vibrations due to the piezoelectric properties of dual piezoelectric materials, which dramatically accelerates the electron transfer and suppresses the recombination of between electrons and holes. This work provides a new approach to constructing photoelectrodes with effective piezoelectric photocatalytic properties.

Interfacial Se-O Bonds Modulating Spatial Charge Distribution in FeSe2/Nb:Fe2O3 with Rapid Hole Extraction for Efficient Photoelectrochemical Water Oxidation

Surface engineering is an effective strategy to improve the photoelectrochemical (PEC) catalytic activity of hematite, and the defect states with abundant coordinative unsaturation atoms can serve as anchoring sites for constructing intimate connections between semiconductors. On this basis, we anchored an ultrathin FeSe2 layer on Nb5+-doped Fe2O3 (FeSe2/Nb:Fe2O3) via interfacial Se-O chemical bonds to tune the surface potential. Density functional theory (DFT) calculations indicate that amorphous FeSe2 decoration could generate electron delocalization over the composite photoanodes so that the electron mobility was improved to a large extent. Furthermore, electrons could be transferred via the newly formed Se-O bonds at the interface and holes were collected at the surface of electrode for PEC water oxidation. The desired charge redistribution is in favor of suppressing charge recombination and extracting effective holes. Later, work function calculations and Mott-Schottky (M-S) plots demonstrate that a type-II heterojunction was formed in FeSe2/Nb:Fe2O3, which further expedited carrier separation. Except for spatial carrier modulation, the amorphous FeSe2 layer also provided abundant active sites for intermediates adsorption according to the d band center results. In consequence, the target photoanodes attained an improved photocurrent density of 2.42 mA cm-2 at 1.23 V versus the reversible hydrogen electrode (RHE), 2.5 times as that of the bare Fe2O3. This study proposed a defect-anchoring method to grow a close-connected layer via interfacial chemical bonds and revealed the spatial charge distribution effects of FeSe2 on Nb:Fe2O3, giving insights into rational designation in composite photoanodes.

Construction of [NbO]6-x -xS Structure to Change Charge Density and Regulate Spontaneous Polarization to Achieve Efficient Pyro-Photo-Electric Water Splitting System of NaNbO3

Pyroelectric materials in the field of photoelectrochemical (PEC) water splitting still face the problems of difficult low spontaneous polarization intensity and excessive carrier recombination. Based on the above problems, we altered the interaction between S-Nb-S in the [NbO]6-x -xS structure, and the constructed [NbO]6-x -xS structure achieved the regulation of charge density change and spontaneous polarization. The results show that under the stimulation of light and temperature fluctuations, the current density of the NS-4 photoanode is as high as 0.574 mA/cm2 at 1.23 VRHE , which is about 1.59 times higher than the pure NaNbO3 current density value, and the NS -4 photoanode achieves IPCE value of 16.08 %. The first-principles density-functional theory calculations (DFT) reveal the principle of the [NbO]6-x -xS structure for the suppression function of the carrier recombination and the improvement function of the pyroelectric effect. The analysis shows that the S-doping leads to the weakening of S-Nb-S interactions in the [NbO]6-x -xS structure, which improves the pyroelectric effect and suppresses the photo/pyro-generated carrier recombination, and effectively enhances the performance of the pyro-photo-electric synergistic water splitting system. This work promotes the development of pyroelectric materials in the field of photoelectrochemical water splitting.

Synergy Effect of the Enhanced Local Electric Field and Built-In Electric Field of CoS/Mo-Doped BiVO4 for Photoelectrochemical Water Oxidation

Bismuth vanadate is a promising material for photoelectrochemical water oxidation. However, it suffers from a low quantum efficiency, poor stability, and slow water oxidation kinetics. Here, we developed a novel photoanode of CoS/Mo-BiVO4 with excellent photoelectrochemical water oxidation performance. It achieved a photocurrent density of 4.5 mA cm-2 at 1.23 V versus the reversible hydrogen electrode, ∼4 times that of BiVO4. The CoS/Mo-BiVO4 photoanode also exhibited good stability, and the photocurrent density generated by the CoS/Mo-BiVO4 photoanode did not significantly decrease after light irradiation for 2 h. Upon replacement of part of the V with Mo doping in BiVO4, the local electric field around the Mo-O bond was enhanced, thus promoting carrier separation in BiVO4. The CoS was deposited on the surface of Mo-BiVO4, forming a built-in electric field at the interface. Under the action of the bias electric field and the built-in electric field, the carriers of CoS/Mo-BiVO4 were efficiently separated in the direction of the inverse type II heterojunction. In addition, CoS improved the light absorption and charge injection efficiency of the CoS/Mo-BiVO4 photoanode.