Rational Construction of Pt Incorporated Co3O4 as High-Performance Electrocatalyst for Hydrogen Evolution Reaction.

Electrocatalysts in alkaline electrocatalytic water splitting are required to efficiently produce hydrogen while posing a challenge to show excellent performances. Herein, we have successfully synthesized platinum nanoparticles incorporated in a Co3O4 nanostructure (denoted as Pt-Co3O4) that show superior HER activity and stability in alkaline solutions (the overpotentials of 37 mV to reach 10 mA cm-2). The outstanding electrocatalytic activity originates from synergistic effects between Pt and Co3O4 and increased electron conduction. Theoretical calculations show a significant decrease in the ΔGH* of Co active sites and a remarkable increase in electron transport. Our work puts forward a special and simple synthesized way of adjusting the H* adsorption energy of an inert site for application in HER.

Tensile Strain-Mediated Spinel Ferrites Enable Superior Oxygen Evolution Activity.

Exploring efficient strategies to overcome the performance constraints of oxygen evolution reaction (OER) electrocatalysts is vital for electrocatalytic applications such as H2O splitting, CO2 reduction, N2 reduction, etc. Herein, tunable, wide-range strain engineering of spinel oxides, such as NiFe2O4, is proposed to enhance the OER activity. The lattice strain is regulated by interfacial thermal mismatch during the bonding process between thermally expanding NiFe2O4 nanoparticles and the nonexpanding carbon fiber substrate. The tensile lattice strain causes energy bands to flatten near the Fermi level, lowering eg orbital occupancy, effectively increasing the number of electronic states near the Fermi level, and reducing the pseudoenergy gap. Consequently, the energy barrier of the rate-determining step for strained NiFe2O4 is reduced, achieving a low overpotential of 180 mV at 10 mA/cm2. A total water decomposition voltage range of 1.52-1.56 V at 10 mA/cm2 (without iR correction) was achieved in an asymmetric alkaline electrolytic cell with strained NiFe2O4 nanoparticles, and its robust stability was verified with a voltage retention of approximately 99.4% after 100 h. Furthermore, the current work demonstrates the universality of tuning OER performance with other spinel ferrite systems, including cobalt, manganese, and zinc ferrites.

Carbon nanotubes encapsulating Pt/MoN heterostructures for superior hydrogen evolution.

Achieving efficient hydrogen evolution reaction (HER) catalysts to scale up electrochemical water splitting is desirable but remains a major challenge. Here, nitrogen-doped carbon nanotubes (NCNTs) loaded with PtNi/MoN electrocatalyst (PtNi/MoN@C) is synthesized by a simple strategy to obtain stronger interphase effects and significantly improve HER activity. The surface morphology of the materials is altered by Pt doping and the electronic structure of MoN is changed, which optimizing the electronic environment of the materials, shifting the binding energy and giving the materials a higher electrical conductivity, this ultimately leads to faster proton and electron transfer processes. The synergistic effect of Pt nanoparticles, MoN and the good combination with carbon leads to a high HER activity of 18 mV to reach 10 mA cm-2 in alkaline solution, outperforming that of the commercial Pt/C. Theoretical studies show that the heterostructures can efficiently enhance the electron transport and reduce the △GH*.

Radial phased-locked Laguerre-Gaussian correlated schell-model beam array.

A new beam array called radial phased-locked Laguerre-Gaussian correlated Schell-model (LGCSM) beam array is presented, the beamlet of this beam array is partially coherent beam with Laguerre Gaussian-Schell model correlation. The propagation expression of a radial phased-locked LGCSM beam array in free space is derived. It is aimed to give the effect of beam parameters on evolutions of beam array composed by LGCSM beam. The radial phased-locked LGCSM beam array has unique properties on propagation, the intensity of such beam array will evolve from a beam array composed of Gauss beams into a beam array formed of LGCSM beams. Furthermore, the intensity evolutions of such beam array are modulated by coherence length and beam order of beamlets. The obtained results are important in areas such as light field shaping, and free space optical communication.

Surface activation towards manganese dioxide nanosheet arrays via plasma engineering as cathode and anode for efficient water splitting.

Developing high-efficiency, low-cost electrocatalysts for water splitting is important but challenging. Two-dimensional nanosheet manganese dioxide (MnO2) arrays are promising candidates for the design and development of advanced catalysts because of their large surface area. Here, a feasible solution to improve the catalytic activity of MnO2 materials via decorating the active sites on the surface is proposed. With the help of plasma engineering, we successfully enabled surface activity of the MnO2 nanosheets by decorating P or Fe species together with rich vacancies on the surface. The decorated P (P-MnO2) or Fe (Fe-MnO2) species were highly beneficial for the absorption of protons and OH- respectively, and rich oxygen vacancies induced the formation of stable Mn3+, which contributed to electron and charge transfer. Thus, increased electrochemically active specific areas, accelerated charge transfer, and a proper surface electronic structure could be achieved. On the basis of this activation strategy, the fabricated P-MnO2 and Fe-MnO2 showed excellent catalytic performance for the hydrogen evolution and oxygen evolution reactions. To our knowledge, the performance of P-MnO2 and Fe-MnO2 outperformed most MnO2-based electrocatalysts in the field of electrocatalytic water splitting. Surface activation of two-dimensional MnO2 materials by decorating active species via plasma treatment can provide a feasible route for modulating the performance of earth-abundant electrocatalysts for practical applications.

Plasma-induced surface reorganization of porous Co3O4-CoO heterostructured nanosheets for electrocatalytic water oxidation.

Herein, porous Co3O4-CoO heterostructured nanosheets are constructed by plasma treatment. The density-functional theory calculations demonstrate that constructing Co3O4-CoO heterostructures modify the electronic structure to achieve enhanced electrical conductivity, but also boost the charge transfer to realize enhanced surface reactivity. Contributing to the short ion diffusion path, the rich electroactive surface sites and enhanced charge transfer capability, the resulting Co3O4-CoO nanosheet arrays possess the low overpotential of 270 mV at 10 mA cm-2 and the low Tafel slope of 49 mV dec-1. This work provides a novel strategy to construct heterostructured nanosheet arrays by surface reorganization for cost-effective OER electrocatalyst.

Rich P vacancies modulate Ni2P/Cu3P interfaced nanosheets for electrocatalytic alkaline water splitting.

Constructing well-defined interfaces is vital to improve the electrocatalytic properties, but the studies on transition-metal-interface electrocatalysts with rich vacancies are rarely reported. Here, rich P vacancies to modulate Ni2P/Cu3P interfaced nanosheets for overall water splitting is demonstrated. We conduct a series of experimental parameters to adjust the nanostructures of Ni2P/Cu3P, and to get insight into the synergistic effects of interfaces and P vacancies on the catalytic activities. Notably, Ni2P/Cu3P with rich P vacancies shows the lowest overpotential requirements of 88 and 262 mV at 10 mA cm-2 towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The good activity is ascribed to abundant electroactive sites, electric field effect at the interfaces and tuning the electron structure by P vacancies. In addition, as bifunctional electrode, Ni2P/Cu3P with rich P vacancies allows for a low water-splitting voltage of 1.60 V at 10 mA cm-2. This work may open up a new route for efficient electrocatalysts through the synergistic effects of interfaces and vacancies.

Free-standing porous Ni2P-Ni5P4 heterostructured arrays for efficient electrocatalytic water splitting.

Constructing heterointerfaces in heterostructures could effectively enlarge the electroactive sites and enhance the interfacial charge transfer, and thus improve the electrocatalytic performances. Herein, free-standing porous Ni2P-Ni5P4 heterostructured arrays are successfully prepared through in situ phosphating Ni(OH)2 arrays by simply tuning the reaction temperatures. Contributing from the interfacial coupling effects of two phases, large surface areas, highly conductive support of carbon cloth substrates and unique free-standing arrays, Ni2P-Ni5P4 heterostructured arrays show the enhanced kinetics and electrocatalytic performances for the hydrogen evolution reaction, oxygen evolution reaction and overall water splitting. Our research might offer insight into constructing heterophase junctions for efficient overall water splitting.

Bifunctional Electrocatalysts Based on Mo-Doped NiCoP Nanosheet Arrays for Overall Water Splitting.

Rational design of efficient bifunctional electrocatalysts is highly imperative but still a challenge for overall water splitting. Herein, we construct novel freestanding Mo-doped NiCoP nanosheet arrays by the hydrothermal and phosphation processes, serving as bifunctional electrocatalysts for overall water splitting. Notably, Mo doping could effectively modulate the electronic structure of NiCoP, leading to the increased electroactive site and improved intrinsic activity of each site. Furthermore, an electrochemical activation strategy is proposed to form Mo-doped (Ni,Co)OOH to fully boost the electrocatalytic activities for oxygen evolution reaction. Benefiting from the unique freestanding structure and Mo doping, Mo-doped NiCoP and (Ni,Co)OOH show the remarkable electrochemical performances, which are competitive among current researches. In addition, an overall water splitting device assembled by both electrodes only requires a cell voltage of 1.61 V to reach a current density of 10 mA cm-2. Therefore, this work opens up new avenues for designing nonprecious bifunctional electrocatalysts by Mo doping and in situ electrochemical activation.

Designing and constructing core-shell NiCo2S4@Ni3S2 on Ni foam by facile one-step strategy as advanced battery-type electrodes for supercapattery.

Herein, we successfully design and construct core-shell nanostructured NiCo2S4@Ni3S2 directly on Ni foam by a scalable and effective one-step strategy. Further, through simply and accurately controlling the concentration of sulfur source, various nanostructures of NiCo2S4@Ni3S2 arrays in situ on Ni foam are successfully synthesized. The intriguing core-shell structures and integrated electrode configurations endow NiCo2S4@Ni3S2 electrode a large electroactive sites, fast electron transport path and sufficient contacts with electrolyte. Serving as free-standing electrode, as-fabricated NiCo2S4@Ni3S2 arrays exhibit the high specific capacity (4.55 C cm-2 at 5 mA cm-2), good rate performance and good cycling stability. Impressively, current research provides a general, scalable and effective one-step strategy for constructing core-shell nanostructures for energy storage devices.