High Charge Transfer Efficiency Research Articles

Ultrafine Mo-Doped Co2P Nanorods Anchored on Reduced Graphene Oxide as Efficient Electrocatalyst for the Hydrogen Evolution Reaction**Supported by the National Natural Science Foundation of China (Grant Nos. 11874027, 11774124, and 11504126) and the China Postdoctoral Science Foundation (Grant Nos. 2019T120233 and 2017M621198).

One-dimensional (1D) transition metal phosphides (TMPs) with large specific surface areas, high charge transfer efficiency and excellent electrical conductivity have attracted significant attention in hydrogen evolution reaction (HER) as versatile and active catalysts. Herein, the sub-4 nm Mo-Co2P ultrafine nanorods (NRs) anchored on reduced graphene oxide (rGO) were successfully synthesized by a colloidal mesostructured strategy. Electrochemical test results reveal that the Mo-Co2P@rGO electrode exhibits superior activity with overpotentials of 204 mV and Tafel slope of 88 mV/dec for HER at 10 mA/cm2, relative to the Co2P@rGO electrode in 0.5 M H2SO4 solution. This improvement could be ascribed to the Mo doping, which results in more active sites, higher electrical conductivity and faster electron-transfer rates. This versatile strategy will provide a promising pathway for transition metal-doped compounds as an efficient catalyst.

Ultrafast Responsive Non‐Volatile Flash Photomemory via Spatially Addressable Perovskite/Block Copolymer Composite Film

AbstractThe exotic photophysical properties of organic–inorganic hybrid perovskite with long exciton lifetimes and small binding energy have appeared as promising front‐runners for next‐generation non‐volatile flash photomemory. However, the long photo‐programming time of photomemory limits its application on light‐fidelity (Li‐Fi), which requires high storage capacity and short programming times. Herein, the spatially addressable perovskite in polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO)/perovskite composite film as an photoactive floating gate is demonstrated to elucidate the effect of morphology on the photo‐responsive characteristics of photomemory. The chelation between lead ion and PEO segment promotes the anti‐solvent functionalities of the perovskite/PS‐b‐PEO composite film, thus allowing the solution‐processable poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) to act as the active channel. Through manipulating the interfacial area between perovskite and P3HT, fast photo‐induced charge transfer rate of 0.056 ns−1, high charge transfer efficiency of 89%, ON/OFF current ratio of 104, and extremely low programming time of 5 ms can be achieved. This solution‐processable and fast photo‐programmable non‐volatile flash photomemory can trigger the practical application on Li‐Fi.

Analysis and Modeling of Spill Back Effect in High Illumination CMOS Image Sensors

To improve charge transfer efficiency ( CTE ) and eliminate image lag, the impact of spill back effect on image lag is studied in CMOS image sensors (CISs), particularly in high illumination condition. By establishing a mathematical model based on the thermionic emission and drift-diffusion theory, the physical mechanism of spill back effect is described. This model shows that a lower transfer gate (TG) operating voltage and a higher reset voltage of Floating Diffusion (FD) node would mitigate spill back effect. In a $0.18\mu \text{m}$ CMOS process, by setting that the gate voltage of transfer transistor and the reset voltage of FD is 2.8 V and 3.8 V respectively, CTE of the proposed pixel is increased to 100%. The theoretical analysis and TCAD simulation results can explain spill back effect and offer a reference for designing a high CTE pixel in high illumination CISs.

TiO2 Nanorods Co‐decorated with Metal‐Free Carbon Materials for Boosted Photoelectrochemical Water Oxidation

AbstractThe key challenge for solar water oxidation is to develop photoanodes with high charge transfer and separation efficiency as well as rapid surface reaction kinetics. Herein, the double metal‐free carbon materials, including carbon dots (CDs) and ultra‐thin carbon nitride (UCN), were coupled with TiO2 nanorods (CDs/UCN/TiO2) to enhance photoelectrochemical (PEC) activity. Attributed to the integrated effect of UCN and CDs, the designed ternary CDs/UCN/TiO2 photoanode exhibits a photocurrent density of 1.43 mA cm−2, which is 3.0‐fold higher than that of the bare TiO2 nanorods. In detail, the UCN can efficiently accelerate the charge separation and restrict the electron/hole recombination, owing to the close contact heterojunction. Meanwhile, the CDs can significantly facilitate H2O2 decomposition, as demonstrated by scanning electrochemical microscopy (SECM), as they induce rapid reaction kinetics. Importantly, such constructed photoanodes modified with double metal‐free carbon materials provide great potential for future progress in PEC water splitting through a simple decoration strategy with metal‐free carbon materials.

The effect of group-substitution on the sensitization properties of alkynylrhenium(I) tricarbonyl diimine complexes adsorbed to TiO2(101) film surface: a theoretical study.

A series of dyes are designed by adding the different electron-donating (-CH3, -NH2, -OH) and electron-withdrawing groups (-Br, -Cl, -NO2) to the different ancillary ligands in the alkynylrhenium(I) tricarbonyl diimine complexes [Re(CO)3(N^N){C≡C-C6H4-CH=C(CN)(COOH)}], where N^N = 1,10-phenanthroline (phen)(1) and then investigated the sensitization properties of dyes linked to the TiO2(101) surface. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to study the electronic structure, frontier molecular orbitals, and absorption spectral properties. The effect of group-substitution on sensitization properties is obvious. When the dye molecules are combined with TiO2(101) surface, not only the absorptions of some sensitizers containing -CH3 or -OH groups have red shift but also the electrons can be directly injected into the TiO2 conduction band from the dye molecules compared with the parent molecular 1. The results indicate that the designed dyes containing electron-donating groups have smaller energy gaps, better light-harvesting efficiency, sufficient driving force, and higher charge transfer efficiency as appropriate dye sensitizers. We hope it can provide valuable hints so that we can design more efficient dye sensitizers in DSSCs.

Enhanced visible-light photocatalytic degradation and disinfection performance of oxidized nanoporous g-C3N4via decoration with graphene oxide quantum dots

Oxidized nanoporous g-C3N4 (PCNO) decorated with graphene oxide quantum dots (ox-GQDs) was successfully prepared by a facile self-assembly method. As co-catalysts, the ultrasmall zero-dimensional (0D) ox-GQDs can achieve uniform dispersion on the surface/inner channels of PCNO, as well as intimate contact with PCNO through hydrogen bonding, π-π, and chemical bonding interactions. In contrast with PCNO, the ox-GQDs/PCNO composite photocatalysts possessed improved light-harvesting ability, higher charge-transfer efficiency, enhanced photooxidation capacity, and increased amounts of reactive species due to the upconversion properties, strong electron capturing ability, and peroxidase-like activity of the ox-GQDs. Therefore, the visible-light photocatalytic degradation and disinfection performances of the ox-GQDs/PCNO composite were significantly enhanced. Remarkably, the composite with a 0.2 wt.% deposited amount of ox-GQDs (ox-GQDs-0.2%/PCNO) exhibited optimum amaranth photodegradation activity, with a corresponding rate about 3.1 times as high as that of PCNO. In addition, ox-GQDs-0.2%/PCNO could inactivate about 99.6% of Escherichia coli (E. coli) cells after 4 h of visible light irradiation, whereas only ˜31.9% of E. coli cells were killed by PCNO. Furthermore, h+, •O2−, and •OH were determined to be the reactive species generated in the photocatalytic process of the ox-GQDs/PCNO system; these species can thoroughly mineralize azo dyes and effectively inactivate pathogenic bacteria.

Construction of 2D/2D Heterogeneous of ZIF‐8/SnS2 Composite as a Transfer of Band‐Band System for Efficient Visible Photocatalytic Activity

AbstractConstructing two‐dimensional (2D) heterostructured nanocomposites is an effective method to boost photo‐generated carrier separation efficiently using layer material. In this work, a tightly coupled 2D/2D ZIF‐8/SnS2 nanosheet heterogeneous composite was successfully prepared. Due to the good heterogeneous interface between 2D SnS2 and 2D ZIF‐8 nanosheet, 2D/2D ZIF‐8/SnS2 nanocomposites formed a large contact interface, leading to high efficient interfacial charge transfer efficiency and shortening the distance of charge transmission. As a result, the optimized SnS2/2D‐ZIF‐8 composites possess excellent photocatalytic properties and the rate of degradation toward MB under visible light for 100 minutes is 2.32 and 26.75 times than that of pure SnS2 and 2D‐ZIF‐8, respectively. This work offers an efficient way to design 2D/2D heterojunction composites as visible‐light‐driven catalyst for the photocatalytic application.

Interfacial growth of the optimal BiVO4 nanoparticles onto self-assembled WO3 nanoplates for efficient photoelectrochemical water splitting

Photoelectrochemical water splitting is the most efficient green engineering approach to convert the sun light into hydrogen energy. The formation of high surface area core-shell heterojunction with enhanced light-harvesting efficiency, elevated charge separation, and transport are key parameters in achieving the ideal water splitting performance of the photoanode. Herein, we demonstrate a first green engineering interfacial growth of the BiVO4 nanoparticles onto self-assembled WO3 nanoplates forming WO3/BiVO4 core-shell heterojunction for efficient PEC water splitting performance. The three different WO3 nanostructures (nanoplates, nanobricks, and stacked nanosheets) were self-assembled on fluorine doped tin oxide glass substrates via hydrothermal route at various pH (0.8–1.2) of the solutions. In comparison to nanobricks and stacked nanosheets, WO3 nanoplates displayed considerably elevated photocurrent density. Moreover, a simple and low cost green approach of modified chemical bath deposition technique was established for the optimal decoration of a BiVO4 nanoparticles on vertically aligned WO3 nanoplates. The boosted photoelectrochemical current density of 1.7 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination was achieved for the WO3/BiVO4 heterojunction which can be attributed to a suitable band alignment for the efficient charge transfer from BiVO4 to WO3, increased light harvesting capability of outer BiVO4 layer, and high charge transfer efficiency of WO3 nanoplates.

Effects of ZnSe modification on the perovskite films and perovskite solar cells based on ZnO nanorod arrays

ZnO as electron transfer layer in perovskite solar cells (PSCs) has a lot of advantages including high electron mobility and low processing temperature. However, because of the reported instabilities of perovskite layers deposited on ZnO, the application of ZnO in perovskite solar cells has been restricted. In this paper, highly ordered ZnO nanorod arrays have been synthesized by a polymer soft template method, and then modified by ZnSe via a successive ion layer adsorption and reaction method (SILAR). Field emission scanning electron microscope, X-ray diffractometer, UV–vis spectrophotometer, fluorophotometer and photovoltaic measurements were used to study the effects of ZnSe modification on the morphology, structure, light absorption and charge transfer of perovskite films and the performance of the PSCs based on ZnO nanorod arrays. The photoelectric conversion efficiency (PCE) of the PSC with ZnSe modification significantly enhanced by 27%, as compared to that of the pristine one, which is attributed to the suitable band alignment, better carrier separation and higher charge transfer efficiency with ZnSe modification. Meanwhile, ZnSe modification can also improve the air stability of the PSCs. This study promotes the development of ZnO nanorod arrays based PSCs with some new approaches and provides a useful reference.

Enhancement of visible-light-driven photocatalytic performance of BiOBr nanosheets by Co2+ doping

In this work, Co2+ modification influence on the visible-light-induced photocatalytic performance of BiOBr was investigated. BiOBr and Co2+-doped BiOBr (Co/BiOBr) nanosheets were fabricated through a facile solvothermal way. The morphology, structure, chemical composition and optical properties of the photocatalysts were characterized by various techniques. The results confirmed the successful synthesis of Co/BiOBr nanosheets and indicated the doped Co2+ had little influence on the surface morphology and crystal structure but expanded the light absorption region. Photoelectrochemical measurements were applied to evaluate the semiconducting properties of Co/BiOBr, and the results implied that compared with the undoped sample, Co/BiOBr had higher charge transfer efficiency and smaller charge transfer resistance which were beneficial to the improvement of visible-light-driven photocatalytic performance. The as-synthesized Co/BiOBr nanosheets exhibited excellent catalytic activity and stability in the photodecomposition of contaminants.

Improved photoelectrochemical performance by forming a ZnO/ZnS core/shell nanorod array

ZnO nanorod arrays (NRAs) were prepared via a facile hydrothermal method for photoelectrochemical (PEC) applications. Then, ZnS thin shell layers were deposited onto them via a facile hydrothermal treatment process for constructing a ZnO/ZnS core/shell structure. It was demonstrated that the PEC activity of a ZnO NRA is enhanced significantly after the surface modification, although there weren’t any obvious changes in the visible-light harvesting efficiency. Both the Nyquist and Mott-Schottky (M-S) plots were employed to reveal the reason, which was attributed to higher electrocatalytic activity of ZnS than that of ZnO and the resulting higher charge transfer efficiency across the solid/liquid interfaces. Finally, a schematic band model was proposed for clarifying the charge carrier transfer mechanism occurred at the interfaces.

Construction of 2D/2D porous graphitic C3N4/SnS2 composite as a direct Z-scheme system for efficient visible photocatalytic activity

Rapid recombination of photoexcited carriers has always been a severe problem that inhibits photocatalytic activity. Designing two-dimensional (2D) heterostructured nanocomposite using layer material is regarded as an effective method to obtain advanced photocatalyst. In this work, we designed novel 2D/2D porous graphitic C3N4/SnS2 (Pg-C3N4/SnS2) composite by in-situ growth of SnS2 onto Pg-C3N4 sheets. The 2D Pg-C3N4 nanosheets were coupled with 2D SnS2 nanosheets forming a large-scale contact interface, leading to high efficient interfacial charge transfer efficiency and shortening the distance of charge transmission. According to the experiments, the optimized Pg-C3N4/SnS2 composite exhibits the highest apparent pseudo-first-order rate constant kapp of 0.14321 min−1 with the content of 10%Pg-C3N4, which exceeds the rates of pure Pg-C3N4 and SnS2 for approximately 18 and 8 times, respectively. On the basis of radical-trapping experiment and band structure analysis, we confirm that the Z-scheme heterojunction was formed between SnS2 and Pg-C3N4. The electrons in SnS2 CB transfer and combine with the holes in the Pg-C3N4, which is beneficial to the spatial separation of photoinduced carriers and strengthen the redox capacity of the photocatalyst. This work supplies an efficient way to design 2D/2D heterojunction for the photocatalytic application.

Electrostatic self-assembly of 2D delaminated MXene (Ti3C2) onto Ni foam with superior electrochemical performance for supercapacitor

The existence of the oxygen-containing functional groups on MXene surface makes it a potential electrode material in supercapacitor based on a redox mechanism. However, the irreversible stacking of MXenes will lead to an insufficient utilization of these functional groups. To solve this problem, we fabricated a composite electrode comprised of 2D delaminated Ti3C2 sheets (d-Ti3C2) and 3D Ni foam (NF) by electrostatic self-assembly. In this electrode, d-Ti3C2 nanosheets are adsorbed on the surface of 3D Ni foam skeleton structure, eliminating the need for insulative polymer binders. The self-assembly strategy endows d-Ti3C2/NF composites with unique 2D/3D structure which possesses the merits of excellent conductivity, sufficient active sites, high charge transfer efficiency and short ions diffusion path. As a result, the d-Ti3C2/NF composite electrode exhibits a high specific capacitance up to 654 F g−1 at 1 A g−1 and good cycling stability. An asymmetrical supercapacitor with d-Ti3C2/NF composite as a positive electrode, bulk Ti3C2 (b-Ti3C2) as a negative electrode and 6 M KOH as electrolyte, exhibits a maximum energy density of 18.1 Wh kg−1 (at 397.8 W kg−1) and excellent cycling stability (80.6% after 5000 cycles). The results indicate that d-Ti3C2/NF composite is a promising electrode material for practical energy storage devices.

Fabrication of Tubular g‐C3N4 with N‐Defects and Extended π‐Conjugated System for Promoted Photocatalytic Hydrogen Production

AbstractSemiconductor photocatalytic hydrogen evolution from water splitting using solar energy is one of the most potential strategies for settling the energy crisis, but a bottleneck is occurred in developing a highly efficient photocatalyst. Herein, we successfully fabricated a tubular g‐C3N4 with nitrogen defects (including both nitrogen vacancies and cyano groups) and extended π‐conjugated system, wherein the nitrogen defects and extended π‐conjugated system were conveniently introduced during thermal polymerization of the pyridinium alkaline ionic liquid‐modified hydrogen‐bonding melamine‐cyanuric acid supramolecular (PHMCS) pre‐aggregates towards carbon nitride with hexagonal cylinder morphology formed by the pyridinium alkaline ionic liquid‐assisted hydrothermal process of low‐cost melamine, in which the added trace pyridinium alkaline ionic liquid serves as an all‐rounder with three roles including the promoting agent towards the transformation of melamine to cyanuric acid for constructing PHMCS, nitrogen defects making agent, and the electronic‐tuning agent regarding of the as‐formed carbon nitride. The tubular structure enhances the light scattering and improves the accessibility of active sites. Meanwhile, the high charge transfer efficiency, broad optical absorption region, and suitable energy band positions are related to both the introduction of nitrogen defects by alkali of ionic liquid and the extended π‐electron delocalization in the conjunction carbon nitride networks. As a consequence, the resulted carbon nitride using optimized amount of pyridinium alkaline ionic liquid (AIL‐2.0‐CN) photocatalyst exhibited a high hydrogen evolution rate of 1284 μmol h−1 g−1 (λ>420 nm) with an apparent quantum efficiency of 4.2 % at 420 nm, which is 13.6 times higher than that of bulk g‐C3N4 (B−CN), and even 3.5 folds much higher than the one (SHPY−CN) prepared by the similar process to that for AIL‐2.0‐CN except for the replacement of pyridinium alkaline ionic liquid by a mixture containing a corresponding amount of pyridine and sodium hydroxide, suggesting the promoting effect resulting from the unique characteristic of pyridinium alkaline ionic liquid. Based on the unique physicochemical properties and the molecules‐ adjustability, the developed alkaline ionic liquid assisted strategy can open an avenue for designing and preparing excellent g‐C3N4 based photocatalysts with tunable geometric and electronic structures for solar hydrogen production.

Ni3(PO4)2 nanoparticles decorated carbon sphere composites for enhanced non-enzymatic glucose sensing

The Ni3(PO4)2/CSs composite microspheres were synthesized via a simple two step hydrothermal process. The composition and morphology of the microspheres were characterized by SEM, TEM, EDS, XRD and XPS. The Ni3(PO4)2 nanoparticles with diameter less than 10 nm have been uniformly decorated on the carbon spheres. The formation mechanism of the Ni3(PO4)2/CSs and their corresponding glucose sensing process have also been proposed. The as prepared Ni3(PO4)2/CSs showed greatly enhanced performance for glucose sensing than that of Ni3(PO4)2, which may be due to the synergistic effect of Ni3(PO4)2 nanoparticles and carbon spheres resulting in a high efficiency of charge transfer. The Ni3(PO4)2/CSs modified electrodes exhibited excellent glucose sensing performance, with wide linear range of (5 μM–2.5 mM) and (2.5 mM–7.5 mM), and corresponding sensitivity of 480.153 μAmM−1cm−2 and 219.898 μAmM−1cm−2. The detection limit of the Ni3(PO4)2/Cs/GCE is found to be 1.67 μM (S/N = 3). Moreover, satisfactory results were also obtained using the as prepared sensor to analyze glucose concentration in serum samples. These results showed that Ni3(PO4)2/CSs can be a favorable electrochemical sensing material for constructing the non-enzymatic sensors.

Analysis of the charge transfer and separation in electrically doped organic semiconductors by electron spin resonance spectroscopy

Abstract We investigated the charge generation mechanism of electrically doped organic semiconductors (OSs) by electron spin resonance (ESR) analysis. ESR spectroscopy was used to successfully evaluate the radical density of p-doped OSs to estimate the charge transfer efficiency (CTE) of various doped systems. The results showed that the CTE is efficient close to 100% if the dopant molecules are homogenously dispersed and the energy difference (ΔE) between the highest occupied molecular orbital (HOMO) level of the host molecule and lowest unoccupied molecular orbital (LUMO) level of the p-dopant is large. The charge separation efficiency to form free carriers from the radicals is rather low (less than 12% in this study) and is a dominant factor controlling the charge generation efficiency (CGE). An organic dopant molybdenum tris[1,2-bis(trifluoromethyl)ethane-1,2-dithiolene] turns out to be an efficient dopant with the CGE of 9.7% due to high CTE originating from homogenous dispersion of the organic p-dopants and low LUMO level, i.e., large ΔE.

Heavy-atom-free charge transfer photosensitizers: Tuning the efficiency of BODIPY in singlet oxygen generation via intramolecular electron donor-acceptor interaction

To test the tunability of charge transfer (CT)-based BODIPY photosensitizers in generating singlet oxygen (1Δg), twelve meso-phenyl-BODIPY (donor-acceptor) type compounds have been synthesized and fully characterized, in which the phenyl moiety is modified with respective 0, 1, 2 and 3 methoxy groups to increase its electron-donating ability. The UV-Vis absorption spectra, fluorescence emission spectra, fluorescence quantum yield, fluorescence lifetime, excited triplet state formation, and singlet oxygen formation properties are measured. DFT quantum chemical computation is also carried out to explain the experiments. The occurrence of intra-molecular CT is confirmed by UV-Vis absorption, fluorescence properties and quantum chemical computation. The triplet excited state formation is evidenced by laser flash photolysis technique. The quantitative photosensitized singlet oxygen formation is demonstrated by DPBF (diphenylisobenzofuran) chemical trapping method.This type of BODIPY CT photosensitizers show good tunability in generating singlet oxygen (1Δg). When the number of methoxy group on the donor is increased (so that CT is enhanced), the efficiency of singlet oxygen generation becomes higher from 0.070 to 0.30. When solvent polarity is increased (CT is also enhanced), the efficiency of singlet oxygen generation is also increased significantly. The increase in singlet oxygen generation is accompanied by the decrease in fluorescence quantum yield and fluorescence lifetime values. These facts show that a higher CT efficiency in a simple phenyl-BODIPY donor-acceptor conjugate can lead to significant higher quantum yield of singlet oxygen generation. These results are useful in designing novel CT-based heavy-atom-free photosensitizers for photodynamic therapy of tumor.

Shell thickness dependent photocatalytic activity of EDTA-assisted Ag/ZnO core-shell nanoparticles under sunlight irradiation

Functionalized Ag/ZnO core–shell (CS) nanoparticles (NPs) with ethylenediaminetetraacetic acid (EDTA) having same core size but with different shell thickness are successfully prepared through a simple and low cost wet chemical process. Different physiochemical characterizations including transmission electron microscopy, x-ray diffraction, Brunauer-Emment-Teller surface area analysis, zeta potential analysis, thermal gravimetric-differential analysis, UV-visible absorption spectroscopy, Photoluminescence Spectroscopy and Fourier-transform infrared Spectroscopy have been involved to characterize the samples. The thickness of ZnO shell of Ag/ZnO CS NPs is found to be increasing with increasing molar ratio of EDTA/Zn2+. The LSPR wavelength of Ag core is shifting to longer visible wavelength with increasing the shell thickness of Ag/ZnO CS NPs because of the increase in the dielectric constant of the sourrounding environment. The increasing shell thickness of Ag/ZnO CS NPs makes a strong effect on the decrease in the fluorescence intensity of UV emission of ZnO. This quenching of PL intensity has been further verified by transient fluorescence (FL) spectra. The Nyquist plots also provide evidence of higher electron-transfer rate of the Ag/ZnO CS NPs of having higher shell thickness. The photocurrent measurement confirms electron-charging of Ag core in Ag/ZnO CS NPs. Variation of concentration of EDTA as anionic surfactant causes variation of surface charge of Ag/ZnO CS NPs. With increasing the shell thickness, photodegradation efficiency of Ag/ZnO CS NPs towards methylene blue (MB) degradation enhances under sunlight irradiation. This enhancement in photocatalytic efficiency with increasing the shell thickness is achieved due to the higher surface area, higher charge transfer efficiency, extended light absorption towards visible region and more negative zeta potential of Ag/ZnO CS NPs.

Co2P Nanoparticles Wrapped in Amorphous Porous Carbon as an Efficient and Stable Catalyst for Water Oxidation.

Exploring highly active, enduringly stable, and low-cost oxygen evolution reaction catalysts continues to be a dominant challenge to commercialize renewable electrochemical water-splitting technology. High-active and earth-abundant cobalt phosphides are recently considered as promising candidates. However, the poor inherent electron transfer efficiency and instability hinder its further development. In this work, a novel approach was demonstrated to effectively synthesize Co2P nanoparticles wrapped in amorphous porous carbon framework (Co2P/C). Benefiting from extremely high specific surface area of porous carbon, plenty of active sites were adequately exposed. Meanwhile, unique anchoring structure between Co2P nanoparticles and amorphous carbon outerwear insured high charge transfer efficiency and superior stability of Co2P/C. Due to these favorable properties, low overpotential of 281 mV at 10 mA cm−2 and Tafel slope of 69 mV dec−1 were achieved in resultant Co2P/C catalyst. More significantly, it only exhibited a negligible overpotential increase after 30 h stability test, and these performances entirely preceded commercial RuO2 benchmark. In summary, we proposed a simple and feasible strategy to prepare metal phosphides wrapped with amorphous porous carbon outerwear for efficient and durable electrochemical water oxidation.

Controllable synthesis of Co2P nanorods as high-efficiency bifunctional electrocatalyst for overall water splitting

One-dimensional transition metal phosphides with large specific surface areas and efficient conductivity have the great potential in both hydrogen and oxygen evolution reaction (HER and OER) as bifunctional catalysts, which are at the heart of water splitting. Herein, we firstly report the controllable synthesis of Co2P nanorods through a substrate- and template-free facile phosphating reaction. Electrochemical test results reveal that the synthesized Co2P nanorods exhibit superior bifunctional activity with overpotentials of 87 mV for HER and 310 mV for OER at 10 mA cm−2, respectively, relative to Co2P/CoP branched nanostructure, CoP nanoparticles and commercial Co2P in alkaline media. In addition, the bifunctional Co2P nanorods catalysts enable overall water splitting with a cell voltage of 1.65 V to achieve 10 mA cm−2 and stabilized potentials at different current densities testing over 24 h. Further analysis demonstrate that the remarkably bifunctional activity is contributed to high charge transfer efficiency, large contact area with electrolyte and a large number of exposed active sites provided by the rod-like nanostructure. This work should shed light on an industrialized pathway for the future design of phosphide catalysts to apply to overall water splitting even other emerging energy devices.