Engineering g-C_(3)N_(4)based materials for advanced photocatalysis:Recent advances

Photocatalysis driven by abundant yet intermittent solar energy has considerable potential in renewable energy generation and environmental remediation.The outstanding electronic structure and physicochemical properties of graphitic carbon nitride(g-C_(3)N_(4)),together with unique metal-free characteristic,make them ideal candidates for advanced photocatalysts construction.This review summarizes the up-to-date advances on g-C_(3)N_(4)based photocatalysts from ingenious-design strategies and diversified photocatalytic applications.Notably,the advantages,fabrication methods and limitations of each design strategy are systemically analyzed.In order to deeply comprehend the inner connection of theory–structure–performance upon g-C_(3)N_(4)based photocatalysts,structure/composition designs,corresponding photocatalytic activities and reaction mechanisms are jointly discussed,associated with introducing their photocatalytic applications toward water splitting,carbon dioxide/nitrogen reduction and pollutants degradation,etc.Finally,the current challenges and future perspectives for g-C_(3)N_(4)based materials for photocatalysis are briefly proposed.These design strategies and limitations are also instructive for constructing g-C_(3)N_(4) based materials in other energy and environment-related applications.

Heteroatom-Induced Accelerated Kinetics on Nickel Selenide for Highly Efficient Hydrazine-Assisted Water Splitting and Zn-Hydrazine Battery

Hydrazine-assisted water electrolysis is a promising energy conversion technology for highly efficient hydrogen production.Rational design of bifunctional electrocatalysts,which can simultaneously accelerate hydrogen evolution reaction(HER)/hydrazine oxidation reaction(HzOR)kinetics,is the key step.Herein,we demonstrate the development of ultrathin P/Fe co-doped NiSe_(2) nanosheets supported on modified Ni foam(P/Fe-NiSe_(2)) synthesized through a facile electrodeposition process and subsequent heat treatment.Based on electrochemical measurements,characterizations,and density functional theory calculations,a favorable“2+2”reaction mechanism with a two-step HER process and a two-step HzOR step was fully proved and the specific effect of P doping on HzOR kinetics was investigated.P/Fe-NiSe_(2) thus yields an impressive electrocatalytic performance,delivering a high current density of 100 mA cm^(−2) with potentials of−168 and 200 mV for HER and HzOR,respectively.Additionally,P/Fe-NiSe_(2) can work efficiently for hydrazine-assisted water electrolysis and Zn-Hydrazine(Zn-Hz)battery,making it promising for practical application.

Mesoporous carbons as metal-free catalysts for propane dehydrogenation: Effect of the pore structure and surface property

Nanocarbon materials have been used as important metal-free catalysts for various reactions including alkane dehydrogenation.However,clarifying the active sites and tuning the nanocarbon structure for direct dehydrogenation have always been significantly challenging owing to the lack of fundamental understanding of the structure and surface properties of carbon materials.Herein,mesoporous carbon materials with different pore ordering and surface properties were synthesized through a soft-templating method with different formaldehyde/resorcinol ratios and carbonization temperatures and used for catalytic dehydrogenation of propane to propylene.The highly ordered mesoporous carbons were found to have higher catalytic activities than disordered and ordered mesoporous carbons,mainly because the highly ordered mesopores favor mass transportation and provide more accessible active sites.Furthermore,mesoporous carbons can provide a large amount of surface active sites owing to their high surface areas,which is favorable for propane dehydrogenation reaction.To control the surface oxygenated functional groups,highly ordered mesoporous carbons were carbonized at different temperatures(600,700,and 800℃).The propylene formation rates exhibit an excellent linear relationship with the number of ketonic C=O groups,suggesting that C=O groups are the most possible active sites.

N-doped porous carbon hollow microspheres encapsulated with iron-based nanocomposites as advanced bifunctional catalysts for rechargeable Zn-air battery

The design and development of low-cost,efficient,and stable bifunctional electrocatalysts for the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are desirable for rechargeable metal-air batteries.In this work,N-doped porous hollow carbon spheres encapsulated with ultrafine Fe/Fe3O4 nanoparticles(FeOx@N-PHCS)were fabricated by impregnation and subsequent pyrolysis,using melamine-formaldehyde resin spheres as self-sacrifice templates and polydopamine as N and C sources.The sufficient adsorption of Fe3+on the polydopamine endowed the formation of Fe-Nx species upon high-temperature carbonization.The prepared FeOx@N-PHCS has advanced features of large specific surface area,porous hollow structure,high content of N dopants,sufficient Fe-Nx species and ultrafine FeOx nanoparticles.These features endow FeOx@N-PHCS with enhanced mass transfer and considerable active sites,leading to high activity and stability in catalyzing ORR and OER in alkaline electrolyte.Furthermore,the rechargeable Zn-air battery with FeOx@N-PHCS as air cathode catalyst exhibits a large peak power density,narrow charge-discharge potential gap and robust cycling stability,demonstrating the potential of the fabricated FeOx@N-PHCS as a promising electrode material for metal-air batteries.This new finding may open an avenue for rational design of bifunctional catalysts by integrating different active components within all-in-one catalyst for different electrochemical reactions.

Phosphonate-derived nitrogen-doped cobalt phosphate/carbon nanotube hybrids as highly active oxygen reduction reaction electrocatalysts

The exploration of cost-effective non-noble-metal electrocatalysts is highly imperative to replace the state-of-the-art platinum-based catalysts for oxygen reduction reaction(ORR). Here, we prepared cobalt phosphonate-derived N-doped cobalt phosphate/carbon nanotube hybrids(Co Pi C-N/CNTs) by hydrothermal treatment of N-containing cobalt phosphonate and oxidized carbon nanotubes(o-CNT) followed by high-temperature calcination under nitrogen atmosphere. The resultant Co Pi C-N/CNT exhibits a superior electrocatalytic performance for the ORR in alkaline media, which is equal to the commercial Pt/C catalyst in the aspect of half-wave potential, onset potential and diffuse limiting current density. Furthermore, the excellent tolerance to methanol and strong durability outperform those of commercial Pt/C. It is found that cobalt phosphonate-derived N-doped cobalt phosphate and the in-situ formed graphitic carbons play key roles on the activity enhancement. Besides, introducing a suitable amount of CNTs enhances the electronic conductivity and further contributes to the improved ORR performance.

Fabrication strategies of porous precious-metal-free bifunctional electrocatalysts for overall water splitting:Recent advances

Electrocatalytic water splitting using power generated from renewable energy to produce hydrogen has been considered as one of the more attractive approach to alleviate the problems of energy crisis and environmental pollution.One of the biggest challenges for the large-scale application of water electrolysis is the searching of the low cost electrocatalysts with high and stable activity toward both hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).The well-developed porous features of materials synthesized from the earth abundant elements endow them with the enhanced mass transfer and improved electronic interconnection during electrochemical reactions,resulting in the excellent electrocatalytic performance for both OER and HER.Herein,this review focuses on the recent development of innovation strategies for the fabrication of porous non-noble-metal materials including heteroatom-doped carbon-based and transition metal(mainly Co,Ni,and Fe)-based materials as efficient electrocatalysts for overall water splitting.Specially,a detailed discussion of the structure–activity correlation gives an insight on the origin of the high electrocatalytic performance of porous materials obtained from different strategies,and provides guidance for future design and preparation of highly efficient electocatalysts based on non-precious carbon or metal materials for overall water splitting.

Facile synthesis of Mo2C nanoparticles on N-doped carbon nanotubes with enhanced electrocatalytic activity for hydrogen evolution and oxygen reduction reactions

Developing low-cost and highly-efficient electrocatalysts for renewable energy conversion technologies has attracted even-increasing attention. Molybdenum carbide materials have recently emerged as a type of promising catalysts for electrocatalytic reactions due to the earth-abundance and Pt-resembled electrical properties. In this work, taking the advantage of the interaction between the basic groups of the Mo(VI)-melamine polymer and the acidic groups on the surface of the oxidized carbon nanotubes(CNTs), N-doped CNTs supported Mo2C nanoparticles(Mo2C/NCNT) are prepared, which exhibit outstanding electrocatalytic activity and durability for both the hydrogen evolution and oxygen reduction reactions. The impressive performance of Mo2C/NCNT can be attributed to the small size of Mo2C particles, the large exposure ratio of surface sites and the presence of N-doped CNTs. This work enlarges the multi-field applications of molybdenum carbide-base materials as promising non-precious metal electrocatalysts, which is of great significance for sustainable energy-related technologies.

Facile synthesis of molybdenum carbide nanoparticles in situ decorated on nitrogen-doped porous carbons for hydrogen evolution reaction

Molybdenum-based electrocatalysts are promising candidates of platinum (Pt)-based materials in electrocatalyzing hydrogen evolution reaction (HER), due to their cost-efficient and resembled electronic properties. Reported herein is the preparation of molybdenum carbide nanoparticles uniformly decorated on nitrogen-modified carbons (Mo2C/NC) through the carbonization of Mo-based polymers under hydrogen atmosphere by using poly(p-phenylenediamine) and ammonium heptamolybdate polymer analogue as precursors. And the molybdenum nitride nanoparticles loaded on porous N-doped carbons (Mo2N/NC) are also fabricated by calcination the polymer precursors in nitrogen gas. The Mo2C/NC shows more excellent electrocatalytic activity than Mo2N/NC in 0.5 M H2SO4, together with robust long-term durability. The well-crystalline nanoparticles and the increased electron conductivity are the main characters responded for the high catalytic efficiency of the fabricated electrocatalysts. This easily fabrication procedure may provide a facile route to prepare non-noble metal carbide/nitride catalysts featuring wellengineered structural and textural peculiarities for realistic energy conversion system.

Synergistically enhanced activity and stability of bifunctional nickel phosphide/sulfide heterointerface electrodes for direct alkaline seawater electrolysis

Direct electrolysis of seawater to generate hydrogen is an attractive but challenging renewable energy storage technology.Reasonable design of seawater electrolysis catalysts should integrate high activity for hydrogen evolution reaction(HER)/oxygen evolution reaction(OER)and enhanced physical/electrochemical stability in seawater.Herein,we demonstrate the development of a Ni foam(NF)supported interfacial heterogeneous nickel phosphide/sulfide(Ni_(2)P/NiS_(2))microsphere electrocatalyst(NiPS/NF)through a facile electrodeposition and subsequent phosphorization/sulfuration process.After NiS_(2)modification,a charge redistribution on the heterointerface is demonstrated and a more advantageous covalent nature of the Ni-P bond is obtained for more easily adsorption of H*and H_(2)O.The NiPS/NF thus yields an impressive electrocatalytic performance in 1.0 M KOH,requiring small overpotentials of 169 and 320 mV for HER and OER to obtain a high current density of 100 m A cm^(-2),respectively.The NiPS/NF can also work efficiently in alkaline seawater with negligible activity degradation,requiring overpotentials of only 188 and 344 mV for a current density of 100 m A cm^(-2)for HER and OER,respectively.A synergistically enhanced physical/electrochemical long-term stability NiPS/NF in saline water is also demonstrated.

Charge redistribution caused by sulfur doping of bimetal FeCo phosphides supported on heteroatoms-doped graphene for Zn-air batteries with stable cycling

Exploring feasible synthesis approaches to highly efficient and robust bifunctional electrocatalysts toward both oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)is triggering researcher’s even-increasing interest in rechargeable Zn-air batteries.Herein,sulfur-doped bimetal FeCo phosphide nanoparticles dispersed on N,P,S-tri-doped graphene(donated as S-FeCo3P/NPSG)are rationally prepared through a controllable one-step carbothermal-phosphorization strategy.The modified charge distribution and electron-donor properties of S-FeCo3P/NPSG caused by S decoration render a significantly beneficial effect on the electrocatalytic activities.Consequently,the S-FeCo3P/NPSG electrode exhibits extraordinary bifunctional activities toward oxygen electrochemistry of the OER overpotential of 290 m V at 10 m A cm^(-2) and the ORR half-wave potential of 0.83 V,approaching to that of noblemetal IrO_(2)(289 m V)and Pt/C(0.84 V),respectively,but with more stronger operation stability in alkaline media.When S-FeCo3P/NPSG serves as the air cathode for liquid-state Zn-air battery,the large peak power density and energy density,as well as superb discharge-charge durability(cycling life>600 h)of this device are obtained.Furthermore,all-solid-state Zn-air battery with S-FeCo3P/NPSG as air electrode also displays excellent mechanical flexibility,high power density and stable cycling stability.The self-reconstruction behavior of the S-FeCo3P/NPSG cathode catalysts is also investigated during the electrocatalytic Zn-air battery operation.This work would provide some novel inspiration from aspects of bonding and charge distribution for the rational construction of active and cost-efficient bifucntional oxygen electrocatalysts for energy storage and conversion devices.

“Charging”the cigarette butt:heteroatomic porous carbon nanosheets with edge-induced topological defects for enhanced oxygen evolution performance

Owing to the complexity of electron transfer pathways,the sluggish oxygen evolution reaction process is defined as the bottleneck for the practical application of Zn-air batteries.In this effort,metal nanoparticles(Co,Ni,Fe,etc.)encapsulated within nitrogen-doped carbon materials with abundant edge sites were synthesized by one-step pyrolysis treatment using cigarette butts as raw materials,which can drastically accelerate the overall rate of oxygen evolution reaction by facilitating the adsorption of oxygenated intermediates by the edge-induced topological defects.The prepared catalyst of nitrogen-doped carbon porous nanosheets loaded with Co nanoparticles(Co@NC-500)exhibits enhanced catalytic activity toward oxygen evolution reaction,with a low overpotential of 350 mV at the current density of 10 mA·cm^(-2).Furthermore,the Zn-air battery assembled with Co@NC-500 catalyst demonstrates a desirable performance affording an open-circuit potential of 1.336 V and power density of 33.6 mW·cm^(-2),indicating considerable practical application potential.

An overview and recent advances in electrocatalysts for direct seawater splitting

In comparison to pure water,seawater is widely accepted as an unlimited resource.The direct seawater splitting is economical and eco-friendly,but the key challenges in seawater,especially the chlorine-related competing reactions at the anode,seriously hamper its practical application.The development of earth-abundant electrocatalysts toward direct seawater splitting has emerged as a promising strategy.Highly efficient electrocatalysts with improved selectivity and stability are of significance in preventing the interference of side reactions and resisting various impurities.This review first discusses the macroscopic understanding of direct seawater electrolysis and then focuses on the strategies for rational design of electrocatalysts toward direct seawater splitting.The perspectives of improved electrocatalysts to solve emerging challenges and further development of direct seawater splitting are also provided.

Interface engineering for boosting electrocatalytic performance of CoP-Co_(2)P polymorphs for all-pH hydrogen evolution reaction and alkaline overall water splitting

Exploring cobalt phosphide catalysts with abundant active sites and outstanding intrinsic activity for active and robust hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)is highly desirable.Herein,by the fine-tuning thermal-reduction treatment of cobalt phosphonates with spherical shape,the novel carbon-wrapped CoP-Co_(2)P polymorphs are rationally constructed.The unique hierarchical porous architecture and heterointerface of CoP-Co_(2)P not only increase active sites but also ensure intrinsic activity.The resultant catalyst exhibits significantly boosted HER activity in a wide pH range,for instance,a current density of 10 mA cm^(-2) at the overpotential of 81 mV in 0.5 mol L^(-1) H_(2)SO_(4),109 mV in 1.0 mol L^(-1) KOH,and 227 mV in 1.0 mol L^(-1) phosphate buffer saline,and remarkable OER activity(1.53 V@10 mA cm^(-2) in 1.0 mol L^(-1) KOH),associated with the impressive stability for each reaction.Moreover,serving as the bifunctional electrocatalysts in a two-electrode electrolyzer for overall water splitting,a low cell voltage of 1.60 V can deliver a current density of 10 mA cm^(-2) in 1.0 mol L^(-1) KOH.The structural evolution process of the CoP-Co_(2)P catalyst during electrolysis is thoroughly investigated.This work presents a new approach for designing and fabricating efficient and affordable metal phosphides for various electrochemical technologies.