Synergistic Coupling of Charge Extraction and Sinking in Cu5FeS4/Ni3S2@NF for Photoassisted Electrocatalytic Oxygen Evolution.

Exploring low-cost and high-performance oxygen evolution reaction (OER) catalysts has attracted great attention due to their crucial role in water splitting. Here, a bifunctional Cu5FeS4/Ni3S2@NF catalyst was in situ formed on a nickel (Ni) foam toward efficient photoassisted electrocatalytic (P-EC) OER, which displays an ultralow overpotential of 260 mV at 30 mA cm-2 in alkaline solution, outperforming most previously reported Ni-based catalysts. It also shows great potential in degradation of antibiotics as an alternative anode reaction to OER owing to the prompt transfer of photogenerated holes. The photocurrent test and transient photovoltage spectroscopy indicate that the synergistic coupling of charge extraction and sinking effects in Cu5FeS4 and Ni3S2 is critical for boosting the OER activity via photoassistance. Electrochemical active surface area and electrochemical impedance spectroscopy tests further prove that the photogenerated electromotive force can effectively compensate the overpotential of OER. This work not only provides a good guidance for integrating photocatalysis and electrocatalysis, but also indicates the key role of synergistic extraction and utilization of photogenerated charge carriers in P-EC.

Nitrogen-doped graphene quantum dots embedding CuCo-LDH hierarchical hollow structure for boosted charge storage capability in supercapacitor.

The nanostructure optimization of layered double hydroxide (LDH) can effectively alleviate fragile agglomerated problems. Herein, nitrogen-doped graphene quantum dots (NGQDs) embedded in CuCo-LDH hierarchical hollow structure is synthesized by hydrothermal and impregnation methods. The electrochemical results show that the ordered multi-component structure could effectively inhibit the aggregation and layer stacking. At the same time, the hierarchical structure establishes new electron and ion transfer channels, greatly reducing the resistance of interlayer transport and accelerating the diffusion rate of electrolyte ions. Besides, NGQDs have both good electrical conductivity and abundant active sites, which can further improve the electron transmission rate and effectively strengthen the energy storage capacity of the material. Therefore, the large specific capacity of 1009 F g-1 can be displayed at 1 A g-1. The energy density of the assembled carbon cloth (CC)@CuCo-LDH/NGQDs//activated carbon (AC) device can reach 58.6 Wh kg-1 at 850 W kg-1. Above test results indicate that CC@CuCo-LDH/NGQDs//AC devices exhibit stable multi-component hierarchical structure and excellent electrical conductivity, which provides an effective strategy for enhancing the electrochemical characteristics of asymmetric supercapacitors.

Ag/Ni-MOF heterostructure with synergistic enrichment and activation properties for electrocatalytic reduction of 4-nitrophenol.

The synchronous optimization of adsorption and activity dominates the practical performance in electrocatalysis, so Ag/Ni-MOF/Ni foam was synthesized for expediting 4-nitrophenol (4-NP) reduction under mild and green conditions. The synergistic combination of selective adsorption (Ni-MOF) and sites (Ag) contributed to the excellent performance of 4-NP reduction. The 4-NP (25 mM) conversion and Faraday efficiency have been achieved up to 98.4% and 99.8%, respectively. Therefore, this work provides a feasible approach for synergistic enrichment and activation to convert pollutants.

Electrocatalytic reduction of 4-nitrophenol over Ni-MOF/NF: understanding the self-enrichment effect of H-bonds.

The chemical adsorption and active sites play a key role in electrocatalysis, so Ni-MOF/nickel foam was fabricated for efficiently reducing 4-nitrophenol (4-NP) without any sacrificial agents. The coordinated water molecules induced the formation of hydrogen bonds (H-bonds) with the nitro group, contributing to the self-enrichment of 4-NP. The reaction rate reached 0.351 µmol min-1 mg-1. Therefore, this work provides a new insight into the H-bond effect in the field of electrocatalysis.

ZIF-8 derived ZnO/TiO2 heterostructure with rich oxygen vacancies for promoting photoelectrochemical water splitting.

Due to the serious recombination of electron-hole and weak photoresponse ability, achieving highly efficient photoelectrochemical (PEC) water splitting activity for TiO2 photoelectrode has become a key issue. In this paper, we reported a new method for preparing ZnO/TiO2 photoelectrodes by electrostatic adsorption from zeolitic imidazolate framework-8 (ZIF-8) as the precursor. ZIF-8 was combined with TiO2 nanorods (NRs) through electrostatic interaction and then calcined to obtain ZnO/TiO2 heterojunction photoelectrodes with abundant oxygen vacancies (Ovac). The introduced ZnO with Ovac provides a large number of active sites which enhanced the electrical conductivity and charges separation of ZnO/TiO2 photoelectrode. The optimal photocurrent density of ZnO/TiO2 photoelectrodes at 1.23 V versus (vs.) reversible hydrogen electrode (RHE) under illumination (100 mW/cm2) has reached 1.76 mA/cm2, almost 2.75 times that of the pure TiO2. Meanwhile, the incident photon-to-electron conversion efficiency (IPCE) of the best photoelectrode has increased to 58.2% at 390 nm, the charge injection (ηinjection) and separation (ηseparation) efficiency have reached to 93.53% and 51.62% (1.23 V vs. RHE), respectively.

Amorphous MnCO3/C Double Layers Decorated on BiVO4 Photoelectrodes to Boost Nitrogen Reduction.

NH3 is mainly obtained by the Haber-Bosch method in the process of industrial production, which is not only accompanied by huge energy consumption but also environmental pollution. The reduction of N2 to NH3 under mild conditions is an important breakthrough to solve the current energy and environmental problems, so the preparation of catalysts that can effectively promote the reduction of N2 is a crucial step. In this work, BiVO4 decorated with amorphous MnCO3/C double layers has been successfully synthesized by a one-step method for the first time. The C and MnCO3 have been formed as ultrathin film, which enables the establishment of a uniform and tight interface with BiVO4. The temperature-programmed desorption of N2 (N2-TPD) spectra confirmed that the MnCO3/C could endow BiVO4 with a drastic enhancement of the chemical absorption ability of a N2 molecule compared with the pristine BiVO4. Meanwhile, the method of isotope labeling proved that the catalyst exhibited excellent selectivity for the photocatalytic nitrogen reduction reaction (NRR). The production rate of NH3 up to 2.426 mmol m-2 h-1 has been achieved over the BiVO4/MnCO3/C, which is almost 8 times that of pristine BiVO4. The promoted production rate of NH3 over BiVO4/MnCO3/C could be mainly attributed to the cooperative process between MnCO3 and C amorphous layers. Therefore, this work could provide an alternative insight to understand the NRR process based on the model of a hierarchical amorphous structure.

Boosted Photoelectrochemical N2 Reduction over Mo2C In Situ Coated with Graphitized Carbon.

Photoelectrochemical N2 reduction reaction (PEC NRR) is a promising method to solve the problems of environmental protection and energy sustainability. However, the strong chemical stability of the N≡N bond and competitive hydrogen evolution reaction (HER) cause the nonideal efficiency of N2 → NH3 conversion in actual operation. For the first time, a Mo2C/C heterostructure was fabricated as a PEC cathode for N2 reduction under environmental conditions. The Mo2C/C heterostructure could effectively decrease the coverage of hydrogen spillover and inhibit the competitive HER, resulting in a desirable selectivity for N2 activation. Meanwhile, the decoration of the C shell further promoted the stability and conductivity of Mo2C. Mo sites of Mo2C were considered as activation centers, which played a dominant role in the final PEC performance. An optimal NH3 yield rate of up to 6.6 µg h-1 mg-1 was achieved with the Mo2C/C heterostructure, which was almost 3 times that with pristine C. The faradic efficiency (FE) of the Mo2C/C heterostructure was 37.2% at 0.2 V (vs Ag/AgCl). This work not only provides an insight into the interplay between the Mo2C/C heterostructure and N2 activation, but also reveals its great potential in NH3 synthesis by a green route.

Ag-Pi/BiVO4 heterojunction with efficient interface carrier transport for photoelectrochemical water splitting.

The limitation of pristine BiVO4 photoanode severely causes the high carrier recombination efficiency and low energy conversion efficiency in the photoelectrochemical (PEC) system. In this work, the Ag-Pi/BiVO4n-n heterojunction has been rationally designed and fabricated for efficient PEC water splitting, through successive ionic layer adsorption reaction method. The built-in field of Ag-Pi/BiVO4 significantly promotes the separation efficiency of photogenerated carriers, benefiting for the participation of abundant holes in water oxidation. The photocurrent density of 40-Ag-Pi/BiVO4 has been enhanced to 2.32 mA/cm2, which is 4.5 times than that of the pristine BiVO4. Compared with the pristine BiVO4 (6.5%), the IPCE value of 40-Ag-Pi/BiVO4 achieves 22% (410 nm, 1.23VRHE). In addition, the charge injection efficiency (ηinjection) and charge separation efficiency (ηseparation) of 40-Ag-Pi/BiVO4 have been achieved to 74.36% (1.23 VRHE) and 31.57% (1.23 VRHE), respectively, revealing the excellent carriers' transfer behavior in the both bulk and interface. The desirable stability endows Ag-Pi/BiVO4 system with a great potential in the practical application in PEC water splitting, and the corresponding mechanism for in-depth understanding the process of carriers' transfer in Ag-Pi/BiVO4 structure has been also proposed. Therefore, the construction of Ag-Pi/BiVO4 heterojunction will provide a new insight for the configuration of efficient PEC system.

Electrodeposition of Cobalt-Phosphate Oxygen Evolution Catalyst on Inert Electrode for Electrolysis.

This study describes the electrodepositon of potentially competent oxygen evolution catalyst on inert anode using phosphate buffered solution containing cobalt ions. The thickness of deposited amorphous cobalt-phosphate catalyst thin film varies depending on the deposition potential and deposition time. The electrodeposited catalyst can actively be used to improve water oxidation reaction under neutral condition.

Effect of Deposition Height on Nanostructure of Tungsten Oxide Thin Films in Flame Vapor Deposition Process.

Vertically aligned nanostructured tungsten oxide thin films have been found useful in many applications due to its intrinsic photonic and electronic properties. In this study, we directly prepared vertically aligned nanostructures including nanowires and nanotubes grown directly on FTO-coated glass by a newly designed flame vapor deposition system. The deposition height was found to be an important parameter for the development of thin film morphology. The evolution of nanowires and nanotubes with time was investigated. Based on our observation, the feasible growth mechanisms of distinct nanostructures were proposed.

Morphology Control of Tungsten Oxide Thin Films in an Aerosol Flame Deposition System.

Tungsten oxide thin film has been found great potential use in various applications such as smart window, gas sensor and photoelectrochemical cell due to their unique electrochromic, gas-chromic and electrochemical properties. The thin film morphology has been considered as an efficient limiting aspect for its performance. In this work, we successfully prepared tungsten oxide thin films with distinctive nanostructures on conductive glass in a flame vapor deposition process. The morphology of tungsten oxide thin films could be controlled by adjusting various process variables, including methane-oxygen ratio, deposition height and support substrate temperature. 1-D nanowires and nanotubes could be obtained in fuel rich flame at high substrate support temperature and 3-D nanocolumns could be easily formed in fuel lean flame. This work offers a rapid, economic approach for the growth of tungsten oxide thin film with controlled morphology.

Flame Synthesized Single Crystal Nanocolumn-Structured WO3 Thin Films for Photoelectrochemical Water Splitting.

Tungsten oxide thin films have been found as an active visible light driven photoanode material for photoelectrochemical water splitting due to its good stability in aqueous solution and energetically favorable valence band position for water oxidation. Morphology control, which determines the performance of WO3 photoanode, is one of most focuses of recent research interests. In this work, we successfully prepared monoclinic WO3 thin films on ITO glass at low range of substrate temperature with a fabrication rate around 100 nm per minute by using aerosol flame deposition process. Single crystal nanocolumns with both triangular pyramid-like and triangular prism-like structure were obtained at certain process conditions. Photoelectrochemical properties of photoelectrodes assembled with both structured WO3 thin films were investigated. The prism-like nanocolumn-structured thin film generated the current density of 1.58 mAcm(-2) at potential of 1.0 V versus Ag/AgCl in 0.5 M H2SO4 solution under illumination of AM 1.5 simulated solar light (100 mVcm(-2)). It presented superior photoelectrochemical performance to pyramid-like nanocolumn-structured WO3 thin film.