Atomically dispersed dinuclear iridium active sites for efficient and stable electrocatalytic chlorine evolution reaction.

The electrochemical chlorine evolution reaction (CER) is a critical anode reaction in chlor-alkali electrolysis. Although precious metal-based mixed metal oxides (MMOs) have long been used as CER catalysts, they suffer from high cost and poor selectivity due to the competing oxygen evolution reaction (OER). Single-atom catalysts (SACs), featuring high atom utilization efficiency, have captured widespread interest in diverse applications. However, the single-atom sites in SACs are generally recognized as independent motifs and the interplay of adjacent sites is largely overlooked. Herein, we report a "precursor-preselected" cage-encapsulated strategy to synthesize atomically dispersed dinuclear iridium active sites bridged by oxygen that are supported on nitrogen-doped carbon (Ir2-ONC). The dinuclear Ir2-ONC catalyst exhibits a CER onset potential of 1.375 V vs. normal hydrogen electrode, a high faradaic efficiency of >95%, and a high mass activity of 14321.6 A gIr -1, much better than the Ir SACs, which demonstrates the significance of coordination and electronic structure regulation for atomically dispersed catalysts. Density functional theory calculations and ab initio molecular dynamics simulations confirm that the unique dinuclear structure facilitates Cl- adsorption, resulting in improved catalytic CER performance.

All-inorganic color converter based on a phosphor in bismuthate glass for white laser diode lighting.

Blue laser diodes (LDs) combined with phosphors have been recognized as the next-generation solid white lighting technology. The phosphor-in-glass (PiG) coating is used for packaging as an appropriate fluorescent conversion material applied to white light LDs. In this work, a low melting point glass Bi2O3-B2O3-ZnO-BaO (BiBZBa), which was mixed with YAG:Ce3+ phosphor powder, was selected as a glass matrix, and the coating of the phosphor in bismuthate glass (PiBG) was successfully fabricated on different substrates through multilayer screen-printing and low-temperature sintering processes. The PiBG-coated substrates were integrated with a 440 nm LD chip in different interlayer structures to obtain PiBG-packaged white laser diodes (WLDs). The thermal performance of Bi2O3-B2O3-ZnO-BaO glass and the phase composition, microstructure, and luminescence properties of PiBG coatings were studied, and the optical performances of WLDs were investigated. When the reflective WLDs were excited by a blue laser with a laser power density of up to 9.3 W mm-2, the related luminous flux (LF), luminous efficiency (LE), and chromaticity coordinates were 3091 lm, 103 lm W-1, and (0.32, 0.32), respectively, indicating great potential in PiBG-packaged high power laser lighting applications.

Investigation of polyethylene glycol (PEG) assisted solvothermal synthesis of CuCoO2 nanosheets for efficient oxygen evolution reaction.

Water splitting to produce hydrogen is known as an effective way to alleviate the energy crisis, but the slow kinetics of the oxygen evolution reaction (OER) has been seriously restricting the development of water splitting technology. Therefore, low cost and high efficiency OER electrocatalysts have become substitutes for traditional noble metal-based catalysts. In this work, CuCoO2 nanosheets (denoted by CCO2) were successfully synthesized under the regulation of surfactants and a solvent polyethylene glycol (PEG) by a solvothermal route using Cu-BTC and Co(NO3)2·6H2O as reactants. The experimental results confirmed that PEG addition could further reduce significantly the crystal size of the CCO2 nanosheets, i.e., the size was about 150 nm and the thickness was 13 nm. The Ni@CCO2 electrode exhibits outstanding OER performance in 1.0 M KOH electrolyte, which shows the overpotential at 10 mA cm-2 is 378 mV, and the Tafel slope is 85 mV dec-1. Moreover, the CCO2 nanosheets exhibit good structural and compositional stability after the 18 h constant current OER test. Therefore, this work may offer a novel insight into enhancing the OER performance of CuCoO2 catalysts by decreasing their crystal size, and using a solvothermal route.

Gram-scale solvothermal synthesis of Fe-doped CuCoO2 nanosheets and improvement of the oxygen evolution reaction performance.

In this work, we used Cu-BTC-IPA and Co(NO3)2·6H2O as precursors to synthesize CuCoO2 (CCO) nanocrystals with a suitable crystal phase, morphology and high yield by changing the process parameters, such as reactant concentration, reactant ratio, mineralizer dosage, and the type of polyvinylpyrrolidone surfactant. In addition, the effects of different concentrations (1 at%, 3 at%, 5 at%) of Fe doping on the crystal structure and oxygen evolution reaction (OER) performance of CCO were studied. The experimental results show that Fe ions are uniformly doped into the lattice to replace the A-site (Cu+) position, which not only reduces the grain size of CCO, but also increases its specific surface area. We further employed the density functional theory (DFT) method to simulate the OER process of transition metal Fe-doped CCO (A-site substitution) and proposed that Fe doping can reduce the Gibbs free energy of each step and promote the formation of each intermediate, thereby improving its OER catalytic performance. In 1.0 M KOH electrolyte, the 3 at% Fe-doped CCO (Ni@3FCCO) electrode has the best OER performance (η10 = 369 mV, Tafel slope = 69 mV dec-1), and the required overpotential to attain 10 mA cm-2 slightly increased (∼30.2 mV) after 18 hours of continuous OER. The crystal morphology and chemical composition did not change significantly before and after the long-term OER test, indicating that the 3FCCO nanosheets have good OER activity and stability. We have proposed two reasons for the significant improvement of OER performance for Fe-doped CCO nanosheets: (1) the partial substitution of Cu cations by Fe cations not only regulates the electronic structure of CCO, making the catalytically active center no longer a single Co site, but also contains the Fe site, thus increasing the number of overall active sites; (2) the synergistic effect between Fe cations and Co cations in the OER process could enhance the activity of a single active site.

Preparation and characterization of nanostructured Fe-doped CoTe2 electrocatalysts for the oxygen evolution reaction.

The key step for hydrogen production through water electrolysis is the development of highly efficient and inexpensive oxygen evolution reaction (OER) catalysts. In this work, we report the successful synthesis of a nanostructured Fe-doped cobalt-based telluride (Fe-doped CoTe2) catalyst on Co foam by a simple one-step hydrothermal synthesis method, which shows excellent OER performance. The influences of Fe doping amounts and reaction temperatures on the morphology, structure, composition, and the OER performance of cobalt-based tellurides have been systematically studied. The optimal sample Co@0.3 g FeCoTe2-200 exhibits a low overpotential of 300 mV at a current density of 10 mA cm-2, and a small Tafel slope of 36.99 mV dec-1, outperforming the undoped cobalt telluride catalysts (Co@CoTe2-200). The Co@0.3 g FeCoTe2-200 electrode also reveals a small overpotential degradation of around 26 mV after an 18-hour continuous OER process. These results unambiguously confirm that Fe doping helps improve the OER activity and long-term catalytic stability. The superior performance of nanostructured Fe-doped CoTe2 can be attributed to the porous structure and the synergistic effect of Co and Fe elements. This study provides a new approach for the preparation of bimetallic telluride catalysts with enhanced OER performance, and Fe-doped CoTe2 holds substantial promise for use as a high-efficiency, cost-effective catalyst for alkaline water electrolysis.

Controllable synthesis of Cu-based quantum dots/nanocrystals and application in white light-emitting diodes.

Lead-free copper-based quantum dots (QDs)/nanocrystals (NCs) with a facile preparation method and low price are promising candidates for replacing traditional expensive phosphors for applications in white light-emitting diodes (W-LEDs). In this article, the strategy of secondary excitation of red CIS/ZnS core-shell QDs using green Cs3Cu2Cl5 NCs and blue Cs3Cu2I5 NCs was employed. UV-excited W-LEDs with a unique (GB)nRm layered structure was successfully prepared using green Cs3Cu2Cl5 NCs, blue Cs3Cu2I5 NCs and red CIS/ZnS core-shell QD composite materials with different luminescence wavelengths. At the same time, the properties of the synthesized CuInS2 (CIS) QDs, CuInS2/ZnS core-shell QDs and Cs3Cu2X5 (X = C1, Br, I) NCs were characterized and the effect of myristic acid (MA) on the optical properties was discussed. This study has an important reference significance on how to use three different quantum dots/nanocrystals to fabricate W-LEDs.

Nanocrystals of CuCoO2 derived from MOFs and their catalytic performance for the oxygen evolution reaction.

In this work, two different solvothermal synthesis routes were employed to prepare MOF-derived CuCoO2 (CCO) nanocrystals for electrocatalytic oxygen evolution reaction (OER) application. The effects of the reductants (ethylene glycol, methanol, ethanol, and isopropanol), NaOH addition, the reactants, and the reaction temperature on the structure and morphology of the reaction product were investigated. In the first route, Cu-BTC derived CCO (CCO1) nanocrystals with a size of ∼214 nm and a specific surface area of 4.93 m2 g-1 were prepared by using Cu-BTC and Co(NO3)2·6H2O as the Cu and Co source, respectively. In the second route, ZIF-67 derived CCO (CCO2) nanocrystals with a size of ∼146 nm and a specific surface area of 11.69 m2 g-1 were prepared by using ZIF-67 and Cu(NO3)2·3H2O as the Co and Cu source, respectively. Moreover, the OER performances of Ni foam supported CCO1 (Ni@CCO1) and CCO2 (Ni@CCO2) electrodes were evaluated in 1.0 M KOH solution. Ni@CCO2 demonstrates a better OER catalytic performance with a lower overpotential of 394.5 mV at 10 mA cm-2, a smaller Tafel slope of 82.6 mV dec-1, and long-term durability, which are superior to those of some previously reported delafossite oxide or perovskite oxide catalysts. This work reveals the preparation method and application potential of CCO electrocatalysts by using Cu-BTC/ZIF-67 as the precursor, providing a new approach for the preparation of delafossite oxide CCO and the enhancement of their OER performances.

Effect of nickel doping on the structure, morphology and oxygen evolution reaction performance of Cu-BTC derived CuCoO2.

In this work, nickel (Ni) doped Cu-BTC derived CuCoO2 (CCO) was successfully synthesized by a solvothermal method, and the effects of Ni doping concentration (such as 1 at%, 3 at% and 5 at%) on the crystal structure, morphology, composition and oxygen evolution reaction (OER) catalytic performance of CuCoO2 were investigated. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were carried out to characterize the crystal structure, morphology and chemical composition of CuCoO2 crystals. The results show that Ni ions have been successfully doped into the CuCoO2 crystal structure and this Ni introduction can reduce its grain size, and 5 at% Ni doped CCO (5NCCO) nanosheets exhibit an average particle size of 386 nm with thicknesses around 28 nm. The optimal Ni@5NCCO electrode needs an overpotential of 409 mV to generate a current density of 10 mA cm-2 and is able to sustain galvanostatic OER electrolysis for 18 hours with only a minor degradation of 30 mV. The enhanced OER performance may be due to the increase in the catalytic activity area and the improvement in conductivity, which is caused by a decrease in grain size and the formation of a porous structure for Ni doped Cu-BTC derived CuCoO2.

Metal-organic framework derived bimetal oxide CuCoO2 as efficient electrocatalyst for the oxygen evolution reaction.

Metal-organic framework (MOF) materials with tunable porous morphology, controlled crystalline structure, various compositions, and high specific surface area are widely used as precursors to synthesize electrocatalysts for water splitting, which is beneficial for improving their oxygen evolution reaction (OER) performance. Using ZIF-67 as a Co source and Cu-BTC as a Cu source, hexagonal MOF-derived CuCoO2 (MOF-CCO) nanocrystals with the size of ∼288 nm were prepared through a one-step solvothermal method. The influence of the content of the precursor solvents (absolute ethanol and deionized water), reaction temperature, mass ratio of reactants, NaOH addition, and reactant concentration of precursors on the structure and morphology of the products was investigated. The optimal CuCoO2 nanocrystals (MOF-CCO1) around 288 nm present the highest OER activity, such as a low overpotential of 364.7 mV at 10 mA cm-2, a small Tafel slope of 64.1 mV dec-1, and attractive durability in 1.0 M KOH solution. The XPS results showed that the higher catalytic efficiency of MOF-CCO1 nanocrystals could be due to the oxygen vacancies caused by lattice oxygen loss, the increase of OH- content on the surface, and the synergistic effect of Cu2+/Cu+ and Co2+/Co3+ redox pairs. Finally, a possible OER mechanism for MOF-CCO nanocrystals of water splitting was proposed. This study provides a new approach for the preparation of delafossite nanomaterials and for the improvement of their OER performances.

Hydrothermal synthesized delafossite CuGaO2 as an electrocatalyst for water oxidation.

Hydrogen production from water splitting provides an effective method to alleviate the ever-growing global energy crisis. In this work, delafossite CuGaO2 (CGO) crystal was synthesized through hydrothermal routes with Cu(NO3)2·3H2O and Ga(NO3)3·xH2O used as reactants. The addition of cetyltrimethylammonium bromide (CTAB) was found to play an important role in modifying the morphology of CuGaO2 (CGO-CTAB). With the addition of CTAB, the morphology of CGO-CTAB samples changed from irregular flake to typical hexagonal sheet microstructure, with an average size of 1-2 µm and a thickness of around 100 nm. Furthermore, the electrocatalytic activity of CGO-CTAB crystals for oxygen evolution reaction (OER) was also studied and compared with that of CGO crystals. CGO-CTAB samples exhibited better activity than CGO. An overpotential of 391.5 mV was shown to be able to generate a current density of 10 mA/cm2. The as-prepared samples also demonstrate good stability for water oxidation and relatively fast OER kinetics with a Tafel slope of 56.4 mV/dec. This work highlights the significant role of modification of CTAB surfactants in preparing CGO related crystals, and the introduction of CTAB was found to help to improve their electrocatalytic activity for OER.

Improved efficiency and carrier dynamic transportation behavior in perovskite solar cells with CuInS2 quantum dots as hole-transport materials.

Inorganic quantum dot (QD)-based hole-transport materials (HTMs) have proved their potential in perovskite solar cells (PSCs). In this work, CuInS2 quantum dots (CIS QDs) were applied as HTMs for PSCs with the architecture of TiO2/Cs0.17FA0.83Pb(Br0.2I0.8)3/HTM/Au. By optimizing the preparation process, a high-quality perovskite thin film could be obtained. When the speed was 5000 rpm, the speed acceleration was 3000 rpm per s and heat treated at 150 °C, the perovskite film had low surface roughness (15.26 nm) and obvious grain boundary. The photoelectric conversion efficiency (PCE) of PSCs was greatly improved from 2.83% to 12.33% utilizing CIS QDs at an optimal concentration and with surface ligands as HTMs. Surface ligands can control the size and shape of CIS QDs, and thus affect the performance of PSCs. The carrier dynamic transportation behaviour at the CIS/perovskite interface was studied, which showed that CIS QDs as HTMs in PSCs can strongly quench the fluorescence and increase the photobleaching recovery rate. Therefore, CIS QDs are promising inorganic HTMs for the fabrication of PSCs.

P-type transparent conducting characteristics of delafossite Ca doped CuScO2 prepared by hydrothermal synthesis.

Ca doped CuScO2 (CSO) delafossite oxides of 3-4 µm were synthesized through the hydrothermal method using Cu(NO3)2·3H2O, Sc(NO3)3·xH2O as the precursor at 240 °C for 24 h in this work. The influence of the process parameters (reaction temperature, Cu/Sc molar ratios, EG (ethylene glycol) quantity, NaOH mineralizer, reactant concentration) on the structure and morphology of CSO was studied systematically. The crystal structure, morphology, and chemical composition of these Ca doped CSO (0, 1 at%, 3 at%, and 5 at%) sheets were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). With increasing Ca dopant, the Ca doped CSO sheets become much thinner; the thickness decreased from 568 nm (CSO) to 190 nm (3 at% Ca doped CSO). Moreover, the conductivity of Ca doped CSO sheets decreased with increasing Ca dopant. The CSO powders (19.91 S m-1) have higher conductivity than Ca doped CSO sheets (9.89, 15.69, and 16.51 S m-1) at room temperature. All these CSO based samples exhibit a weak absorption ability with the absorptance around 20-40% in the visible light region (400-780 nm). The optical band gap values exhibited a blue shift with increasing Ca dopant. The calculated band gaps of Ca-doped CSO sheets are 3.88 eV, 3.91 eV, 3.90 eV and 3.93 eV, respectively. This result indicates that all these CSO based samples have potential applications as p-type transparent materials in optoelectronic devices, owing to their comparable optical transmittance in the UV-vis region.

Discovery of Real-Space Topological Ferroelectricity in Metallic Transition Metal Phosphides.

Ferroelectric metals-with coexisting ferroelectricity and structural asymmetry-challenge traditional perceptions because free electrons screen electrostatic forces between ions, the driving force of breaking the spatial inversion symmetry. Despite ferroelectric metals having been unveiled one after another, topologically switchable polar objects with metallicity have never been identified so far. Here, the discovery of real-space topological ferroelectricity in metallic and non-centrosymmetric Ni2 P is reported. Protected by the rotation-inversion symmetry operation, it is found that the balanced polarity of alternately stacked polyhedra couples intimately with elemental valence states, which are verified using quantitative electron energy-loss spectroscopy. First-principles calculations reveal that an applied in-plane compressive strain creates a tunable bilinear double-well potential and reverses the polyhedral polarity on a unit-cell scale. The dual roles of nickel cations, including polar displacement inside polyhedral cages and a 3D bonding network, facilitate the coexistence of topological polarity with metallicity. In addition, the switchable in-plane polyhedral polarity gives rise to a spin-orbit-coupling-induced spin texture with large momentum-dependent spin splitting. These findings point out a new direction for exploring valence-polarity-spin correlative interactions via topological ferroelectricity in metallic systems with structural asymmetry.

Surfactant-Modified Hydrothermal Synthesis of Ca-Doped CuCoO2 Nanosheets with Abundant Active Sites for Enhanced Electrocatalytic Oxygen Evolution.

It is urgent to explore cost-effective, high-efficiency, and durable electrocatalysts for electrochemical water splitting due to the rapidly increasing energy consumption. In this work, we successfully synthesize Ca-doped CuCoO2 nanosheets (CCCO-P NSs) with different Ca2+ dopants (such as 3, 5, and 10 atom %) by a surfactant-modified hydrothermal reaction with polyvinylpyrrolidone (PVP) addition. The oxygen evolution reaction (OER) performances of these CCCO-P NSs in 1.0 M KOH are investigated. An optimal nickel foam supported CCCO-P2 NSs (Ni@CCCO-P2, 5 atom % Ca-doped) electrode requires low overpotential of 470 mV to afford the current density of 10 mA cm-2 and small Tafel slope of 96.5 mV dec-1. Furthermore, the Ni@CCCO-P2 electrode displays outstanding long-term stability during the galvanostatic OER electrolysis for 18 h with a little degradation of 32 mV. The improvement of OER performances for CCCO-P2 NSs could be attributed to their higher active surface area, more active sites (Co vacancies defect and Co3+/Co4+ redox pairs), and higher electrical conductivity. This work highlights the joint effect of surfactant and Ca doping for preparing CuCoO2 with nanosheet-like morphology and porous crystal structure, which is favorable for enhancing their OER performance.

Self-Epitaxial Hetero-Nanolayers and Surface Atom Reconstruction in Electrocatalytic Nickel Phosphides.

Surface atomic, compositional, and electronic structures play decisive roles in governing the performance of catalysts during electrochemical reactions. Nevertheless, for efficient and cheap transition-metal phosphides used for water splitting, such atomic-scale structural information is largely missing. Despite much effort being made so far, there is still a long way to go for establishing a precise structure-activity relationship. Here, in combination with electron-beam bombardment and compositional analysis, our atomic-scale transmission electron microscopy study on Ni5P4 nanosheets, with a preferential (001) orientation, directly reveals the coverage of a self-epitaxial Ni2P nanolayer on the phosphide surface. Apart from the presence of nickel vacancies in the Ni5P4 phase, our quantum-mechanical image simulations also suggest the existence of an additional NiPx (0 < x < 0.5) nanolayer, characteristic of complex surface atom reconstruction, on the outermost surface of the phosphides. The surface chemical gradient and the core-shell scenario, probably responsible for the passivated catalytic activity, provide a novel insight to understand the catalytic performance of transition-metal catalysts used for electrochemical energy conversion.

Hydrothermal synthesis of delafossite CuScO2 hexagonal plates as an electrocatalyst for the alkaline oxygen evolution reaction.

In recent years, substantial efforts have been devoted to investigating the electrocatalytic activity of transition metal oxide catalysts, especially delafossite oxides have been proved to exhibit remarkable activity toward the oxygen evolution reaction (OER). Herein, the electrocatalytic activity and stability of CuScO2 hexagonal plates (around 3-4 µm) for the OER in alkaline solution were investigated. The micron sized CuScO2 with well-defined hexagonal plate morphology was prepared through a facile hydrothermal method. Moreover, its crystal structure, morphology, surface chemical states, thermal stability, and electrocatalytic performance were studied. The CuScO2 powder exhibits efficient catalytic activity and good long-term stability towards the OER in 1.0 M KOH. An optimal electrode of Ni foam supported CuScO2 powders needs an overpotential of 490 mV to afford a benchmark current density of 10 mA cm-2 and is able to sustain galvanostatic OER electrolysis for 18 hours with little degradation of 33 mV.

High-efficient separation of photoinduced carriers on double Z-scheme heterojunction for superior photocatalytic CO2 reduction.

Developing heterojunction is one of promising approaches to acquire desired photocatalysts with high-efficient photocatalytic activity. In this work, sheet-like ternary ZnO/ZnWO4/g-C3N4 composite was synthesized via stepwise calcination treatment. The double interface electric fields built in the ZnO/ZnWO4/g-C3N4 heterojunction can promote efficient separation of photogenerated charge carriers in space. Moreover, in contrast with the individual ZnO, g-C3N4, ZnWO4 and their binary composites, this double Z-scheme heterojunction achieves more light harvesting, larger pore volume, stronger photoreduction capacity and CO2 adsorption capacity. Therefore, the sheet-like ZnO/ZnWO4/g-C3N4 heterojunction exhibits efficient conversion of the CO2 molecules into solar fuels under the light irradiation. The production yield of photocatalytic CO2 reduction over the double Z-scheme heterojunction is 13.19 µmol h-1 g-1 and the conversion rate of hydrocarbon fuel is highly up to 91.5%, which are much higher than that of other samples. This work offers a novel perspective to achieve high-efficiency heterojunction system for photoredox applications such as photocatalytic antibacterial, nitrogen fixation and degradation of pollutions.

Investigation of the structural, optical and electrical properties of Ca2+ doped CuCoO2 nanosheets.

In this work, we present the hydrothermal synthesis of delafossite oxide Ca-doped CuCoO2 (CCCaO) nanosheets at a low temperature of 100 °C. The crystal phase, morphology and chemical composition of these CuCoO2 (CCO) based samples were comprehensively characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The size of CCCaO nanosheets decreased with increasing Ca dopant concentration, and the optimized CCCaO nanosheets (∼490 nm in lateral size and ∼15 nm in thickness) were much smaller than CCO nanocrystals (∼540 nm in lateral size and 85 nm in thickness). The specific surface area of these CCO based samples increased with increasing Ca content, and the optimized CCCaO nanosheets present a high BET surface area of 28 m2 g-1. XPS and Raman spectroscopy analyses indicate Ca2+ dopant substitution on the Cu+ site in CCCaO nanosheets. Moreover, the effects of Ca2+ doping on the optical and electrical properties of these CCO based samples were further studied. The optical properties measured at room temperature show high absorbability (up to 90%) in the ultraviolet-visible-near infrared (UV-VIS-NIR) region, and the indirect band gap shows a significant blue-shift with increasing Ca2+ concentration. The CCO nanocrystals possess a higher electrical conductivity than the CCCaO nanosheets, and present good conductivities of around 12.81, 4.47 and 0.69 s m-1 for the CCO and CCCaO samples at room temperature. The facile fabrication process, tunable crystallite sizes, and excellent optical absorption and electrical properties of these CCO based nanomaterials are encouraging for the development of future applications in photoelectric devices.

The oxygen evolution reaction enabled by transition metal phosphide and chalcogenide pre-catalysts with dynamic changes.

The oxygen evolution reaction represents an important electrochemical reaction in several energy storage and conversion devices such as water electrolyzers and metal-air batteries. Developing efficient, inexpensive and durable electrocatalysts for the oxygen evolution reaction (OER) has been one of the major focuses of applied electrochemistry and has attracted considerable research attention in the past decades. Non-oxide based transition metal compounds, typically transition metal phosphides (TMPs) and chalcogenides (TMCs), have recently emerged as new categories of OER pre-catalysts, demonstrated outstanding electrocatalytic performance as compared to the conventional oxide- or hydroxide-based OER catalysts for alkaline water electrolysis, and even shown promise to replace noble metals for proton-exchange membrane (PEM) water electrolysis. In this feature article, we will summarize the latest advances in the development of TMP- and TMC-based OER electrocatalysts. In particular, we will discuss the electrochemical stability of TMPs and TMCs predicted using Pourbaix diagrams and their morphological, structural and compositional evolution under OER conditions. We will also point out some challenges to be addressed in this specific area of research and propose further investigations yet to be done.

Hierarchical ZnO Decorated with CeO2 Nanoparticles as the Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Activity.

Development of a high-efficiency heterojunction with an improved photocatalytic property is regarded as a promising way to decontaminate wastewater. Herein, the direct novel Z-scheme heterojunction formed between CeO2 nanoparticles and hierarchical ZnO was synthesized through the wet chemistry method and then the heat-treatment technique. The as-synthesized ZnO/CeO2 composites display highly enhanced photocatalytic rhodamine B (RhB) degradation compared with pristine ZnO and CeO2. Specifically, ZnO/CeO2-3 (mass fraction of CeO2, 30%) shows good photostability and the best removal efficiency for photodegradated RhB, which are almost 2.5 and 1.7 times than pristine ZnO and CeO2, respectively. On the basis of the detailed characterizations and the degradation behavior of as-prepared samples over RhB, the formed heterojunction between the hierarchical ZnO and CeO2 nanoparticles is confirmed as the direct Z-scheme heterojunction. The heterojunction system shows fast transfer, high-efficiency separation, and long lifetime of photoinduced charge carriers, as well as enhanced redox capacity. This study affords a novel approach to construct ZnO-based Z-scheme heterojunctions for the photocatalytic applications.