BiVO4 Film Coupling with CoAl2O4 Nanoparticles for Photoelectrochemical Water Splitting Utilizing Broad Solar Spectrum through p-n Heterojunction, Photothermal, and Cocatalytic Synergism.

Water oxidation is an endothermic and kinetics-sluggish reaction; the research of photoanodes with photothermal and cocatalytic properties is of great significance. Herein, BiVO4/CoAl2O4 film photoanodes were studied for solar water splitting through coupling spinel p-type CoAl2O4 nanoparticles on n-type BiVO4 films. Compared to the BiVO4 photoanode, better performance was observed on the BiVO4/CoAl2O4 photoanode during water oxidation. A photocurrent of 3.47 mA/cm2 was produced on the BiVO4/CoAl2O4 photoanode at 1.23 V vs RHE, which is two-fold to the BiVO4 photoanode (1.70 mA/cm2). Additionally, the BiVO4/CoAl2O4 photoanodes showed an acceptable stability for water oxidation. The BiVO4/CoAl2O4 photoanode being of higher water oxidation performance could be attributed to the presence of p-n heterojunction, cocatalytic, and photothermal effects. In specific, under the excitation of λ < 520 nm light, the holes produced in/on BiVO4 can be transferred to CoAl2O4 owing to the p-n heterojunctions of BiVO4/CoAl2O4. Meanwhile, the temperature on the BiVO4/CoAl2O4 photoanode rises quickly up to ∼53 °C under AM 1.5 G irradiation due to the photothermal property of CoAl2O4 through capturing the 520 < λ < 720 nm light. The temperature rising on the BiVO4/CoAl2O4 photoanode improves the cocatalytic activity of CoAl2O4 and modifies the wettability of BiVO4/CoAl2O4 for effective water oxidation.

Tuning Surface Electronics State of P-Doped In2.77S4/In(OH)3 toward Efficient Photoelectrochemical Water Oxidation.

Indium sulfide with a two-dimensional layered structure offers a platform for catalyzing water oxidation by a photoelectrochemical process. However, the limited hole holders hinder the weak intrinsic catalytic activity. Here, the nonmetallic phosphorus atom is coordinated to In2.77S4/In(OH)3 through a bridge-bonded sulfur atom. By substituting the S position by the P dopant, the work function (surface potential) is regulated from 445 to 210 mV, and the lower surface potential is shown to be beneficial for holding the photogenerated holes. In2.77S4/In(OH)3/P introduces a built-in electric field under the difference of Fermi energy, and the direction is from the bulk to the surface. This band structure results in upward band bending at the interface of In2.77S4/In(OH)3 and P-doped sites, which is identified by density functional theory calculations (∼0.8 eV work function difference). In2.77S4/In(OH)3/P stands out with the highest oxidation efficiency (ηoxi = 70%) and charge separation efficiency (ηsep = 69%). Importantly, it delivers a remarkable water oxidation photocurrent density of 2.51 mA cm-2 under one sun of illumination.

An enhanced electrocatalytic oxygen evolution reaction by the photothermal effect and its induced micro-electric field.

Promoting better thermodynamics and kinetics of electrocatalysts is key to achieving an efficient electrocatalytic oxygen evolution reaction (OER). Utilizing the photothermal effect and micro-electric field of electrocatalysts is a promising approach to promote the sluggish OER. Herein, to reveal the relationship of the photothermal effect and its induced micro-electric field with OER performance, NiSx coupled NiFe(OH)y on nickel foam (NiSx@NiFe(OH)y/NF) is synthesized and subjected to the OER under near-infrared (NIR) light. Owing to the photothermal effect and its induced micro-electric field, the OER performance of NiSx@NiFe(OH)y/NF is significantly enhanced. Compared with no NIR light irradiation, the overpotential at 50 mA cm-2 and the Tafel slope of NiSx@NiFe(OH)y/NF under NIR light irradiation were 234.1 mV and 38.0 mV dec-1, which were lower by 12.4 mV and 7.1 mV dec-1, and it exhibited stable operation at 1.6 V vs. RHE for 8 h with 99% activity maintained. This work presents a novel inspiration to understand the photothermal effect-enhanced electrocatalytic OER.

Mn-Doped M2CdCl4 (M = CH3NH3+, C2H8N+, and C3H10N+) Layered Hybrid Perovskite and Its Flexible Film Based on Simple Mechanochemical Synthesis.

Layered hybrid perovskites show significant advantages in the field of optoelectronics. However, the low quantum efficiency and complex preparation methods limit their applications. In this work, we developed a series of perovskite powders with a two-dimensional (2D) layered structure of organic-inorganic hybrid metal halides M2CdCl4:x%Mn (M = CH3NH3+, C2H8N+, C3H10N+) via facile mechanochemical methods. The prepared manganese Mn-doped MA2CdCl4 produces orange emission at 605 nm under both 254 and 420 nm excitation, which originates from a dual excitation channel competition mechanism, and its excitation channel could be changed with the increase of Mn2+ ion concentration. Typically, MA2CdCl4:20%Mn powder exhibits high photoluminescence quantum yield (PLQY) close to 90% at 605 nm due to the organic amine ions enlarging the Mn-Mn interlayer distances. In addition, we prepared MA2CdCl4:x%Mn@PVA flexible films, which also exhibit good luminescence at 254 nm excitation and were unexpectedly found to have a better response to Cs+, which could be a candidate for anticounterfeiting applications.

Enhanced Oxygen Evolution Reaction Performance on NiSx@Co3O4/Nickel Foam Electrocatalysts with Their Photothermal Property.

Based on the principle of heterogeneous catalysis for water electrolysis, electrocatalysts with appropriate electronic structure and photothermal property are expected to drive the oxygen evolution reaction effectively. Herein, amorphous NiSx-coupled nanourchin-like Co3O4 was prepared on nickel foam (NiSx@Co3O4/NF) and investigated as a electrocatalyst for photothermal-assisted oxygen evolution reaction. The experimental investigations and simulant calculations jointly revealed NiSx@Co3O4/NF to be of suitable electronic structure and high near-infrared photothermal conversion capability to achieve the oxygen evolution reaction advantageously both in thermodynamics and in kinetics. Relative to Co3O4/NF and NiSx/NF, better oxygen evolution reaction activity, kinetics, and stability were achieved on NiSx@Co3O4/NF in 1.0 M KOH owing to the NiSx/Co3O4 synergetic effect. In addition, the oxygen evolution reaction performance of NiSx@Co3O4/NF can be obviously enhanced under near-infrared light irradiation, since NiSx@Co3O4 can absorb the near-infrared light to produce electric and thermal field. For the photothermal-mediated oxygen evolution reaction, the overpotential and Tafel slope of NiSx@Co3O4/NF at 50 mA cm-2 were reduced by 23 mV and 13 mV/dec, respectively. The present work provides an inspiring reference to design and develop photothermal-assisted water electrolysis using abundant solar energy.

Reaction Site Designation by Intramolecular Electric Field in Tröger's-Base-Derived Conjugated Microporous Polymer for Near-Unity Selectivity of CO2 Photoconversion.

To facilitate solar-driven overall CO2 and H2 O convsersion into fuels and O2 , a series of covalent microporous polymers derived from Tröger's base are synthesized featuring flexural backbone and unusual charge-transfer properties. The incorporation of rigid structural twist Tröger's base unit grants the polymers enhanced microporosity and CO2 adsorption/activation capacity. Density function theory calculations and photo-electrochemical analyses reveal that an electric dipole moment (from negative to positive) directed to the Tröger's base unit is formed across two obliquely opposed molecular fragments and induces an intramolecular electric field. The Tröger's base unit located at folding point becomes an electron trap to attract photogenerated electrons in the molecular network, which brings about suppression of carrier recombination and designates the reaction site in synergy with the conjugated network. In response to the discrepancy in reaction pathways across the reaction sites, the product allocation in the catalytic reaction is thereby regulated. Optimally, CMP-nTB achieves the highest photocatalytic CO production of 163.53 µmol g-1 h-1 with approximately unity selectivity, along with H2 O oxidation to O2 in the absence of any photosensitizer or co-catalyst. This work provides new insight for developing specialized artificial organic photocatalysts.

Boosting photocatalytic CO2 reduction via Schottky junction with ZnCr layered double hydroxide nanoflakes aggregated on 2D Ti3C2Tx cocatalyst.

Designing efficient photocatalysts is vital for the photoreduction of CO2 to produce solar fuels, helping to alleviate issues of fossil fuel depletion and global warming. In this work, a novel ZnCr-LDH/Ti3C2Tx Schottky junction is successfully synthesized using an in situ coprecipitation method. ZnCr-LDH nanoflakes collectively grow on the surface of Ti3C2Tx MXene nanosheets. When using Ti3C2Tx MXene as a cocatalyst in the prepared heterojunction, the light absorption intensity, photo-induced electron separation and migration efficiency increase. As a result, the composite ZnCr-LDH/Ti3C2Tx results in significant improvement in the performance of photocatalytic CO2 reduction under simulated solar irradiation. The optimized sample ZCTC25 has the highest photocatalytic CO2 reduction rates of 122.45 µmol g-1 CO and 19.95 µmol g-1 CH4 (after 6 h of irradiation). These values are approximately 2.65 times higher than those of pristine ZnCr-LDH. The product selectivity towards CO is 86%. This work provides a new method for the construction of novel 2D semiconductor photocatalysts and enriches the application of an unusual type of layered double hydroxides in the photoreduction of CO2.

Vacancy-defect modulated pathway of photoreduction of CO2 on single atomically thin AgInP2S6 sheets into olefiant gas.

Artificial photosynthesis, light-driving CO2 conversion into hydrocarbon fuels, is a promising strategy to synchronously overcome global warming and energy-supply issues. The quaternary AgInP2S6 atomic layer with the thickness of ~ 0.70 nm were successfully synthesized through facile ultrasonic exfoliation of the corresponding bulk crystal. The sulfur defect engineering on this atomic layer through a H2O2 etching treatment can excitingly change the CO2 photoreduction reaction pathway to steer dominant generation of ethene with the yield-based selectivity reaching ~73% and the electron-based selectivity as high as ~89%. Both DFT calculation and in-situ FTIR spectra demonstrate that as the introduction of S vacancies in AgInP2S6 causes the charge accumulation on the Ag atoms near the S vacancies, the exposed Ag sites can thus effectively capture the forming *CO molecules. It makes the catalyst surface enrich with key reaction intermediates to lower the C-C binding coupling barrier, which facilitates the production of ethene.

Objective Findings on the K-Doped g-C3N4 Photocatalysts: The Presence and Influence of Organic Byproducts on K-Doped g-C3N4 Photocatalysis.

The thermal-condensation method is widely used for the synthesis of K-doped g-C3N4 photocatalysts, but the presence of organic byproducts in the resultant products is often overlooked in previous reports. Here, we demonstrated the universal presence of organic byproducts in K-doped g-C3N4 synthesized by typical thermal condensation of KOH/melamine, KOH/dicyandiamide, or KOH/urea. Taking the K-doped g-C3N4 photocatalysis for the degradation of dimethyl phthalate as an example, the negative influence of the organic byproducts on K-doped g-C3N4 photocatalysis was confirmed. Specifically, the organic byproducts can be gradually dissolved into the photocatalytic system of K-doped g-C3N4 as new and stable pollutants. Based on the solubility investigations on the byproducts in several solvents, hot-water washing was demonstrated to be a relatively effective approach to remove the organic byproducts from K-doped g-C3N4. The formation of organic byproducts during the synthesis of K-doped g-C3N4 could be ascribed to the fact that the presence of K salts in melamine, dicyandiamide, or urea molecules results in their insufficient thermal condensation into expected g-C3N4. The present work provides objective information about the K-doped g-C3N4 photocatalysts and reminds researchers about the influence of the organic byproducts on the applications of the other impurity-doped g-C3N4 photocatalysts.

Unpaired Electron-Induced Wide-Range Light Absorption within Zn (or Cu) MOFs Containing Electron-Withdrawing Ligands: A Theoretical and Experimental Study.

In photocatalysis, it is of general interest to understand and design wide-range light-absorbing inorganic/organic hybrid materials with an excellent photo-induced intramolecular charge-transfer (ICT) effect. To verify the role of unpaired electrons in enhancing ICT within electron-withdrawing ligand-based metal-organic frameworks (MOFs), the molecular structure, density of states (DOS), and electronic structure of strong electron-deficient pyridine-diketopyrrolopyrrole (P-DPP)-based Zn (or Cu) MOFs were calculated in Gaussian package to validate the unpaired electron ICT. The electron spin resonance technique has detected the unpaired electrons for the coordination systems containing Zn-O or Cu-O clusters and P-DPP ligand on photoexcitation. The estimated band gaps from the DOS calculation for P-DPP-Cu and P-DPP-Zn are 1.4 and 2.4 eV, respectively, showing a good agreement with the experimental UV-vis optical spectra. The partial DOS, dipole moment, and frontier orbital analysis prove that the ICT should happen from Zn-O or Cu-O clusters to P-DPP ligands. This research may contribute to a comprehensive understanding of electron-withdrawing ligand-induced ICT within MOFs and shed light on the design of light-absorbing MOFs with excellent ICT or conductivity.

Anchoring of black phosphorus quantum dots onto WO3 nanowires to boost photocatalytic CO2 conversion into solar fuels.

A 0D-1D direct Z-scheme heterojunction consisting of black phosphorus quantum dots (BPQDs) anchored onto WO3 nanowires was well designed. Kelvin probe force microscopy studies provide direct evidence for charge transfer and separation between BPQDs and WO3 in a single nanowire, confirming the Z-scheme model. The BPQD-WO3 heterojunction displays excellent performance of photocatalytic reduction of CO2, exhibiting not only highly efficient carbon monoxide solar fuel conversion, but also a significant amount of ethylene (C2H4), a highly value-added hydrocarbon species, rarely reported in previous photocatalysis processes. Both experimental and theoretical calculations demonstrate that BPQD plays a critical role in photocatalytic formation of C2H4 from CO2.

Thermodynamic and Kinetic Influence of Oxygen Vacancies on the Solar Water Oxidation Reaction of α-Fe2O3 Photoanodes.

To reveal the role of oxygen vacancies in the solar water oxidation of α-Fe2O3 photoanodes, the kinetic and thermodynamic properties that are closely related to the water oxidation reaction of the α-Fe2O3 photoanode containing oxygen vacancies were investigated. Compared with the pristine α-Fe2O3 photoanode, the presence of surface oxygen vacancies can improve the water oxidation activity and stability of the α-Fe2O3 photoanode simultaneously, but the bulk oxygen vacancies have a negative effect on the water oxidation performance of the α-Fe2O3 photoanode. In thermodynamics, our investigations revealed that the presence of surface oxygen vacancies narrows the space charge region width of the α-Fe2O3 photoanode, which could boost the charge separation and transfer efficiency of the α-Fe2O3 photoanode during water oxidation. Because the surface property and hydrophilicity of α-Fe2O3 are modified owing to the presence of surface oxygen vacancies, the water oxidation kinetics of the α-Fe2O3 photoanode with surface oxygen vacancies is obviously boosted. Our findings in the present work provide comprehensive understanding of the thermodynamic and kinetic differences for α-Fe2O3 photoanodes with and without oxygen vacancies for solar water oxidation.

Cascade cycling of nicotinamide cofactor in a dual enzyme microsystem.

Encapsulation of two enzymes, alcohol dehydrogenase (ADH) and glucose oxidase (GOx), within peroxidase-like tourmaline microparticle (TM)-based colloidosomes was used to construct a functionalized microsystem capable of sustainable cascade cycling of nicotinamide cofactor (NAD+/NADH) via chemical signaling between spatially confined dual-enzyme and active membranes.

Pyridine-Diketopyrrolopyrrole-Based Novel Metal-Free Visible-Light Organophotoredox Catalyst for Atom-Transfer Radical Polymerization.

In the field of electronics, organocatalysts are in high demand for use in the synthesis of clean polymers using solar radiation rather than potentially contaminating metals. Combining theoretical design, simulation, and experiments, this work presents a novel, pyridine-diketopyrrolopyrrole (P-DPP)-based metal-free visible-light organophotoredox catalyst (P-DPP). It is effective in the photocontrolled organocatalytic atom-transfer radical polymerization (O-ATRP) of methyl methacrylate (MMA) and styrene. The use of this catalyst and white light-emitting diode (LED) irradiation produces polymers with a cross-linked feature. In O-ATRP, the P-DPP catalyst has an oxidative quenching catalytic mechanism with an excited-state reductive potential of -1.8 V, fluorescence lifetime of 7.5 ns, and radical-cation oxidative potential of 0.45 V. Through molecular simulation, we found that the adjacent pyridine group is key to reducing the alkyl halide initiator and generating radicals, while the diketopyrrolopyrrole core stabilizes the triplet state of the catalyst through intramolecular charge transfer. The findings related to this novel photoredox catalyst will aid in the search for much more effective organophotoredox catalysts for use in controlled radical polymerization. They will also be of value in the fields of polymer chemistry and physics and in various applications.

Insight into the Kinetic Influence of Oxygen Vacancies on the WO3 Photoanodes for Solar Water Oxidation.

Improvements to solar water oxidation performance for WO3 photoanodes due to oxygen vacancies have in general been ascribed to thermodynamic effects. Detailed insights into the water oxidation kinetics for WO3 photoanodes with oxygen vacancies are still lacking. Here, our experimental and computational investigations revealed that the water oxidation pathway on WO3 photoanodes with oxygen vacancies is more inclined to follow the four-hole pathway. This finding reasonably explained the common observations of higher faradaic efficiency for oxygen evolution, better stability, and faster kinetics for water oxidation usually achieved on the WO3 photoanodes with oxygen vacancies.

Carbon-incorporated porous honeycomb NiCoFe phosphide nanospheres derived from a MOF precursor for overall water splitting.

Developing non-noble metal-based electrocatalysts with high catalytic activity is an urgent task for overall electrocatalytic water decomposition. In this study, carbon-incorporated porous honeycomb NiCoFe phosphide (labelled NiCoFeP/C) was successfully developed from a metal-organic framework (MOF) precursor for the first time. Benefitting from a unique structure and compositional advantages, NiCoFeP/C exhibits excellent bifunctional electrocatalytic activity for the oxygen evolution reaction/hydrogen evolution reaction (OER/HER) in alkaline solution, showing low OER and HER overpotentials of 270 and 149 mV at 10 mA cm-2, respectively. This work successfully developed a MOF-derived novel multi-component transition metal phosphide with a unique structure, which shed some light on the development of promising catalysts for the OER/HER.

Carbon-incorporated NiO/Co3O4 concave surface microcubes derived from a MOF precursor for overall water splitting.

Carbon-incorporated NiO/Co3O4 concave surface microcubes (denoted as NCMC) are successfully developed from a precursor of Ni3[Co(CN)6]2 for the first time. The NCMC exhibits excellent electrocatalytic activity for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) in potassium hydroxide solution, affording a current density of 10 mA cm-2 at 169.5 mV for the HER and 290 mV for the OER, respectively. This communication describes a rational design of MOF-derived mixed metal oxides as electrocatalysts for overall water splitting, promoting the further development of MOF materials in the field of energy conversion.

Highly symmetrical, 24-faceted, concave BiVO4 polyhedron bounded by multiple high-index facets for prominent photocatalytic O2 evolution under visible light.

A highly symmetrical, 24-faceted, concave BiVO4 polyhedron was fabricated, bounded by multiple high-index {012}, {210}, {115}, and {511} facets, exhibiting impressive photocatalytic O2 evolution for water oxidation in the absence of any cocatalysts, more than two orders of magnitude higher than that of the bulk materials. The corresponding apparent quantum yield (AQY) of O2 evolution was measured as high as 30.7% under 420 nm light irradiation, a new record AQY for BiVO4. The high-index facets are not only energetically favorable for water dissociation, but also exhibit an obvious reduction in the overpotential (0.7-1.0 V) for the oxygen evolution reaction.

BiVO4 tubular structures: oxygen defect-rich and largely exposed reactive {010} facets synergistically boost photocatalytic water oxidation and the selective N[double bond, length as m-dash]N coupling reaction of 5-amino-1H-tetrazole.

Unprecedented, oxygen defect-rich, monoclinic BiVO4 nanotubes with largely exposed active {010} facets were successfully fabricated through a self-curling process of nascently generated ultrathin lamellar sheets, exhibiting impressive photocatalytic performance for both water oxidation and the selective N[double bond, length as m-dash]N coupling reaction of 5-amino-1H-tetrazole into sodium 5,5-azotetrazolate, with more than an order of magnitude enhancement relative to bulk materials.

Convincing Synthesis of Atomically Thin, Single-Crystalline InVO4 Sheets toward Promoting Highly Selective and Efficient Solar Conversion of CO2 into CO.

Atomically thin, single-crystalline InVO4 sheets with the uniform thickness of ∼1.5 nm were convincingly synthesized, which was identified with strong, low-angle X-ray diffraction peaks. The InVO4 atomic layer corresponding to 3 unit cells along [110] orientation exhibits highly selective and efficient photocatalytic conversion of CO2 into CO in the presence of water vapor. Surface potential change measurement and liquid photoluminescence decay spectra confirm that the atomically ultrathin structure can shorten the transfer distance of charge carriers from the interior onto the surface and decrease the recombination in body. It thus allows more electrons to survive and accumulate on the surface, which is beneficial for activation and reduction of CO2. In addition, exclusively exposed {110} facet of the InVO4 atomic layer was found to bind the generating CO weakly, facilitating quick desorption from the catalyst surface to form free CO molecules, which provides an ideal platform to catalytically selective CO product.