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As an organic semiconductor, graphitic carbon nitride (g-C3N4) nanosheets have been developed into a highly active photocatalyst for H2O splitting generating H2 under visible light irradiation condition and for reduction of CO2. The photo/electro-chemical performances are dependent on the porous structure, morphology, thickness, and crystallinity of the materials. Construction of g-C3N4 heterojunctions can be vital in enhancing catalytic performances. Instead of focusing on the photocatalysis of g-C3N4 (as in other reviews), this review aims to focus on the photo- and electro-chemical as well as photoluminescence (PL) properties of layered g-C3N4 nanostructured materials with various morphologies. Latest progress in chemical synthesis and engineering of g-C3N4 homo- and hetero-structures are summarized in this review, including exploring (i) the relationship between morphology, composition, crystallinity and thickness of the material; (ii) the construction of homo-/hetero-structures and their band gaps; (iii) photo-/electro-chemical performances; (iv) the possible applications and trends of graphitic carbon nitride materials. The electro-catalytic performance and photoluminescence property of g-C3N4 nanosheets for applications in electrocatalysis and emitting devices are discussed. A variety of versatile properties of g-C3N4 nanomaterials have been constantly discovered recent years. The property evolution and invigorating perspectives on major challenges of layered graphitic carbon nitride are also concluded. [ABSTRACT FROM AUTHOR]

Two-dimensional carbon-based material is attracting considerable attention in exploiting photocatalyst under visible light for photocatalytic energy conversion and storage field, e.g., photocatalytic H2 production, and photodegradation. Here, WS2/WO3 composites are grown on crystalline graphitic carbon nitride (g-C3N4) nanosheets to form heterostructures using a hydrothermal treatment method. While the composition of WS2/WO3 depends on the preparation conditions, the ratio of WS2/WO3 affects the photocatalytic performance of samples. WS2/g-C3N4 heterostructures prepared with addition of ascorbic acid reveal enhanced photocatalytic activity due to efficient separation of photogenerated charge carriers. In contrast, sample with relatively low-WS2 proportion reveals high-H2 generation performance under visible-light irradiation. Under full solar spectrum irradiation, the average H2 evolution rate of sample is increased by 5.7 times comparing with that under visible-light test condition. The electrochemical performance of WS2/WO3/g-C3N4 heterostructures was studied using g-C3N4 with different crystallinity for comparison. With fixed WS2/WO3/g-C3N4 ratio, crystalline g-C3N4 leads to improved photocatalytic activity of WS2/WO3/g-C3N4 heterostructures. Sample using g-C3N4 with the highest crystallinity (prepared at 750 ℃) has the highest photodegradation rate and photocurrent response rate comparing with the samples prepared using low-crystalline g-C3N4 substrate. [ABSTRACT FROM AUTHOR]

g-C3N4 has been used as a photocatalyst to overcome the issues of environmental crises and energy shortages. Here, red g-C3N4 nanosheets (Eg: ∼ 1.89 eV) were used as seeds for the edge-epitaxial growth of yellow g-C3N4 (Eg: ∼ 2.59 eV) to form type II heterostructures. The heterostructures revealed superior photocatalytic activity for enhanced H2 (3996 μmol g−1 h−1), CO (3.8 μmol g−1 h−1), and CH4 (1.8 μmol g−1 h−1) evolution. [ABSTRACT FROM AUTHOR]

g-C3N4 crystalline/amorphous lateral-like homostructures were prepared using crystalline g-C3N4 nanosheets as seeds via sequential edge-epitaxy growth. The homojunction effectively separates photogenerated carriers, resulting in high photo- and electro-catalytic activities. [ABSTRACT FROM AUTHOR]

Nitrogen-doped porous carbon nanocubes with a high surface area synthesized by carbonizing Prussian blue nanocubes coated with poly(fururyl alcohol) were used to support Pt nanoparticles as an electrocatalyst for the oxidation of methanol. The resulting catalyst exhibited excellent electrocatalytic activity and electrochemical stability, owning to its high surface area, a uniform dispersion of Pt particles, and enhanced interaction between the particles and the support. [ABSTRACT FROM AUTHOR]

Abstract: Solid oxide fuel cells (SOFCs) are the most efficient devices for the direct conversion of the chemical energy stored in fuels such as hydrogen and hydrocarbons into electricity. The development of highly efficient and robust SOFCs requires cathodes and anodes with high electrocatalytic activity for O2 reduction and direct oxidation of hydrocarbon fuels, respectively. Nanoscale engineering of electrode structures via metal salt solution impregnation or infiltration attracts increasing attention as the most effective way to develop highly active and advanced electrode structures for SOFCs. The infiltration method opens a new horizon in the advanced electrode development as the method expands the set of variable electrode materials combinations with the elimination of thermal expansion mismatch and the suppression of potential detrimental reactions between electrode and electrolyte materials. In this article, the advances and challenges in the development of nanoscale and nano-structured electrodes and the fundamental understanding of the remarkable enhancement in the electrode performance are reviewed and discussed with primary focus on the progress and status of the field in the last 5 years. [Copyright &y& Elsevier]

The authors have successfully synthesized Pd-on-Pt (thickness: 12 nm) and Au-on-Pt bimetallic nanosheaths on multiwalled carbon nanotubes (MWCNTs) via a seed-mediated growth approach. Pt nanoparticles as seeds were pre-deposited on MWCNTs with uniform distribution followed by the successive seed-mediated growth of metal atoms reduced by a weak reducing agent, ascorbic acid. The essential role of pre-deposited nanoseed particles on MWCNTs was demonstrated. The as-prepared materials were characterization by transition electron microscopy, energy-dispersive X-ray spectroscopy, and element mapping tools. The current strategy extends the classical seed-mediated growth method to prepare bimetallic nanosheath on MWCNT support. [ABSTRACT FROM AUTHOR]

Abstract: Pt and Pd nanosheaths are successfully synthesized on multi-walled carbon nanotubes (MWCNTs) using the non-covalent poly(diallyldimethylammonium chloride) (PDDA) functionalization and seed-mediated growth methods. In this method, negatively charged Pt or Pd metal precursors are self-assembled with positively charged PDDA-functionalized MWCNTs, forming uniformly distributed Pt or Pd nanoseeds on MWCNTs supports. The contiguous and highly porous Pt and Pd nanosheath structured catalysts are then formed by the seed-mediated growth in corresponding metal precursors using ascorbic acid as the reducing agent. The essential role of uniformly dispersed Pt and Pd nanoseeds on PDDA-MWCNTs is demonstrated. The results indicate that both Pt and Pd nanosheaths show an enhanced catalytic activity for the methanol and formic acid oxidation reaction in acid solution, respectively, as compared with conventional Pt/C and Pd/C catalysts. The enhanced activities are most likely due to the reduced oxophilicity, which results in a weakened chemisorption energy with oxygen-containing species such as COad, and the increased reactive sites due to the large number of grain boundaries of the Pt and Pd nanosheath structured electrocatalysts. [ABSTRACT FROM AUTHOR]

Abstract: A palladium-impregnated La0.75Sr0.25Cr0.5Mn0.5O3−δ /yttria-stabilized zirconia (LSCM/YSZ) composite anode is investigated for the direct utilization of methane and ethanol fuels in solid oxide fuel cells (SOFCs). Impregnation of Pd nanoparticles significantly enhances the electrocatalytic activity of LSCM/YSZ composite anodes for the methane and ethanol electrooxidation reaction. At 800°C, the maximum power density is increased by two and eight times with methane and ethanol fuels, respectively, for a cell with the Pd-impregnated LSCM/YSZ composite anode, as compared with that using a pure LSCM/YSZ anode. No carbon deposition is observed during the reaction of methane and ethanol fuels on the Pd-impregnated LSCM/YSZ composite anode. The results show the promises of nanostructured Pd-impregnated LSCM/YSZ composites as effective anodes for direct methane and ethanol SOFCs. [Copyright &y& Elsevier]

It is challenging to construct g-C 3 N 4 (normally as a photocatalyst) with tunable and stable photoluminescence (PL) in solution or in powder form. In this paper, a molten-salt-assisted route has been developed to create red superior thin carbon nitride (g-C 3 N 4) nanosheets with redshifted absorption spectrum and narrowed bandgap of 1.91 eV. Interestingly, these g-C 3 N 4 nanosheets exhibit excellent water soluble nature. The colloidal solution of the nanosheets reveals bright, stable, and tunable PL from blue to yellow. The PL of samples depends on the concentration of g-C 3 N 4 nanosheets. At lower concentration, a blue-emitting band is observed, while a green to yellow emitting band is recorded at higher concentration. Namely, the powder sample reveals a broad green to yellow emitting band. A reversible PL phenomenon is observed by precipitation of g-C 3 N 4 colloidal solution. This phenomenon is ascribed to the assembly of these g-C 3 N 4 nanosheets. The PL efficiency of red-coloured g-C 3 N 4 nanosheets powder is 75%. Both powder and colloidal solution g-C 3 N 4 samples reveal excellent PL stability. The PL intensity and efficiency of the powder samples remain almost unchanged after half year. These water-soluble red g-C 3 N 4 nanosheets thus can be effectively utilized for light emitting diodes and bioimages. [Display omitted] • Porous red g-C 3 N 4 nanosheets was prepared via a salt assisted synthesis. • The colloidal solution of g-C 3 N 4 revealed tunable photoluminescence (PL) from blue to yellow. • The PL of samples depends on the concentration of g-C 3 N 4 nanosheets. • The PL efficiency of red-coloured g-C 3 N 4 nanosheets powder is up to 75%. [ABSTRACT FROM AUTHOR]

The effect of transition metal particle size and distribution on the catalytic performances of carbon nanotubes (CNTs)-based catalysts has been attracting considerable attention in recent years. In this paper, Ni nanoparticles with a Ni 3 C shell structure were embedded in N-doped CNTs by thermal condensation of dicyandiamide with Ni salts followed by MoS 2 nanosheets deposition. Most interesting, dissolution, redistribution and diffusion of the embedded Ni/Ni 3 C nanoparticles take place during the stage of deposition of MoS 2 nanosheets on the CNTs with the help of excess S precursors. The dissolution, redistribution and diffusion result in the disappearance of Ni nanoparticles and formation of much finer Ni nanoclusters, which significantly facilitates the deposition and formation of vertical MoS 2 nanosheets on CNTs. The homogeneous distribution of Ni nanocluster leads to improved intrinsic conductivity and increased active sites. N-doped CNTs with optimized Ni and MoS 2 loading revealed high activity and stability for electrocatalytic hydrogen evolution reaction (HER). The as-prepared MoNiCNTs electrocatalysts exhibit superior HER activity with low onset potential and small Tafel slope value in both acidic and alkaline electrolyte conditions. The result provides a new platform for rational design and fabrication of high-performance non-precious transition metal based HER electrocatalysts. Image 1 [ABSTRACT FROM AUTHOR]

Effect of Gd0.2Ce0.8O1.9 (GDC) infiltration on the performance and stability of La0.8Sr0.2MnO3 (LSM) oxygen electrodes on Y2O3-stabilized ZrO2 (YSZ) electrolyte has been studied in detail under solid oxide electrolysis cell (SOEC) operating conditions at 800 °C. The incorporation of GDC nanoparticles significantly enhances the electrocatalytic activity for oxygen oxidation reaction on LSM electrodes. Electrode polarization resistance of pristine LSM electrode is 8.2 Ω cm2 at 800 °C and decreases to 0.39 and 0.09 Ω cm2 after the infiltration of 0.5 and 1.5 mg cm−2 GDC, respectively. The stability of LSM oxygen electrodes under the SOEC operating conditions is also significantly increased by the GDC infiltration. A 2.0 mg cm−2 GDC infiltrated LSM electrode shows an excellent stability under the anodic current passage at 500 mA cm−2 and 800 °C for 100 h. The infiltrated GDC nanoparticles effectively shift the reaction sites from the LSM electrode/YSZ electrolyte interface to the LSM grains/GDC nanoparticle interface in the bulk of the electrode, effectively mitigating the delamination at the LSM/YSZ interface. The results demonstrate that the GDC infiltration is an effective approach to enhance the structural integrity and thus to achieve the high activity and excellent stability of LSM-based oxygen electrode under the SOEC operating conditions. [ABSTRACT FROM AUTHOR]

Abstract: We reported nano-structured Ag modified Ba0.5Sr0.5Co0.6Fe0.4O3−δ (Ag@BSCF) cathode for solid oxide fuel cells (SOFCs) that is prepared by vacuum assisted electroless deposition technique. We show that the concentration of Ag can be easily adjusted by tuning the deposition time without altering the perovskite structure of the pristine BSCF. The effect of Ag loading on the electrochemical performance of the material has been systematically studied by varying the Ag loading and the working condition (oxygen partial pressure). An optimized electrode performance is observed with an Ag loading of ∼2 wt%. We demonstrate that the presence of Ag significantly reduces the electrode ohmic resistance and enhances the catalytic O2 reduction performance of the BSCF cathode. [Copyright &y& Elsevier]

Abstract: Nano-structured (La,Sr)MnO3 infiltrated Y2O3–ZrO2 (LSM–YSZ) oxygen electrodes show excellent activity and performance stability under solid oxide electrolysis cells (SOECs) operation conditions. LSM–YSZ composite electrodes are prepared by infiltrating pre-sintered YSZ scaffold with LSM nitrate solution, followed by heat-treatment at 900 or 1100°C. The electrodes heat-treated at 900°C exhibit an electrode polarization resistance as low as 0.21Ωcm2 at 800°C and are relatively stable under electrolysis operation at 500mAcm−2 for 100h, while the electrodes heat-treated at 1100°C show the increased stability with the electrolysis polarization. The results clearly indicate that LSM lattice shrinkage under anodic electrolysis conditions inhibits the agglomeration and grain growth of infiltrated LSM nanoparticles, leading to the highly stable nano-structured LSM–YSZ electrode structure. [Copyright &y& Elsevier]

Two dimensional/two dimensional (2D/2D) layered heterostructures possess enhanced photo- and electro-catalytic performances due to large contact area that improves interfacial charge transfer. Herein, 2D/2D WO x /Ni-g-C 3 N 4 and MoS 2 /Ni-g-C 3 N 4 heterostructures are fabricated via mechanical chemical grinding and hydrothermal synthesis, using superior thin N-doped g-C 3 N 4 nanosheets obtained by introducing Ni clusters into bulk g-C 3 N 4 during condensation process. The Ni clusters play the key role in formation of layered heterostructure. WO x consisting mainly of WO 3 and limited amount of WO 2 can be homogeneously distributed onto g-C 3 N 4 nanosheets to form WO x /Ni-g-C 3 N 4 heterostructures. The heterostructure with optimized WO x ratio exhibits enhanced H 2 generation (3.9 mmolg−1h−1) and CO 2 reduction rate (4.2 μmolg−1h−1) that is 3 times higher than that of WO x /g-C 3 N 4 heterostructure with no Ni decoration. The enhanced photocatalytic performances are due to the formation of step-scheme heterojunction. Moreover, similar methods are used for synthesizing MoS 2 /Ni-g-C 3 N 4 heterostructures. In contrast, MoS 2 /Ni-g-C 3 N 4 heterostructure with optimized MoS 2 ratio reveals high stability and activity in electrocatalytic hydrogen evolution reaction (HER). The MoS 2 /Ni-g-C 3 N 4 electrocatalyst exhibits superior HER activity with low onset potential and small Tafel slope value in both acidic and alkaline condition. The results provide new perspectives on designing and constructing novel heterojunction catalysts. • 2D/2D WO x /Ni-g-C 3 N 4 and MoS 2 /Ni-g-C 3 N 4 heterostructures are fabricated. • Ni clusters play the key role in formation of layered heterostructure. • Heterostructures with WO x exhibits enhanced H 2 generation and CO 2 reduction rate. • Heterostructures with MoS 2 reveals high stability and activity in HER. • The result is utilizable on designing novel heterojunction catalysts. [ABSTRACT FROM AUTHOR]

Noble metals in carbon networks dramatically improve the carrier separation and transfer efficiencies of layered graphic carbon nitride (g-C 3 N 4) based heterostructures for efficient CO 2 and benzene photocatalytic conversion. Here, Pt clusters are homogeneously incorporated into ultrathin g-C 3 N 4 nanosheets via multi-step treatment method using the combinations of mechano-chemical pre-reaction and two-step thermal condensation processes. Small Pt nanoparticles with diameters of less than 5 nm are observed and WO x nanobelts with increased oxygen vacancies (as the active sites) are horizontally grown on the thin Pt-g-C 3 N 4 nanosheets. The photocatalytic activities of the constructed composite materials are evaluated under full solar spectrum irradiation condition including water splitting, CO 2 photoreduction, and benzene to phenol conversion. The WO x /Pt-g-C 3 N 4 nanosheet heterostructures with optimized preparation condition and without adding any co-catalyst reveals enhanced H 2 generation (5267 μmolg−1h−1) and CO 2 photoreduction (5.89 and 3.12 μmolg−1h−1 for CO and CH 4 conversion rate, respectively), as well as improved benzene to phenol conversion (89.0%) and selectivity (98.2%). The presence of Pt clusters in the heterostructures improves charge transport in-between g-C 3 N 4 and WO x , thus enhances the charge separation efficiency of the composite material. Detailed photocatalytic mechanisms are discussed on the alteration from S-scheme WO x /g-C 3 N 4 heterostructure to Z-scheme WO x /Pt-g-C 3 N 4 heterostructure. [Display omitted] [ABSTRACT FROM AUTHOR]

Ordered nanostructured cathodes based on controlled vertically aligned Pt nanotubes are fabricated via combining sacrificial template method and in-situ galvanic replacement for ultra-low Pt loading passive direct methanol fuel cells (DMFCs). The Pt nanotubes are composed of highly dispersed Pt nanoparticles shell with an average thickness of ca. 15 nm. Employed as the oxygen reduction reaction (ORR) electrocatalyst, it exhibits similar activity but better durability than that of the commercial Pt black. Serving as the cathode for passive DMFC, a high electrochemical specific area of 77.48 m 2 g −1 (Pt) is obtained by the ordered nanostructured cathode, which is 3 times higher than that of the conventional Pt/C based cathode (19.46 m 2 g −1 (Pt) ), indicating a significant improvement in the Pt catalyst utilization. Impressively, the Pt loading at the cathode side can be reduced to approximately 1/7 (0.12 mgcm −2 ) of the conventional MEA without sacrificing cell performance by using the vertically aligned Pt nanotubes catalytic layer. This method may provide a new way to fabricate ordered nanostructured cathode for ultra-low Pt loadings fuel cells. [ABSTRACT FROM AUTHOR]

• Cu clusters were embedded into graphitic carbon nitride to obtain black nanosheets. • Enhanced ferromagnetism of the black nanosheets is found for the first time. • The black nanosheets reveal enhanced H 2 , CO, and CH 4 generation in visible light. • High conversion rate and high selectivity to phenol achieved for benzene oxidation. Copper (Cu) clusters are incorporated into graphitic carbon nitride (g-C 3 N 4) via a two-step thermal polymerization process, forming a superior thin black g-C 3 N 4 nanosheets based Cu cluster composite (Cu-g-C 3 N 4) with highly efficient charge transfer characteristic and enhanced photocatalytic activity. The Cu–N bonding is formed through intercalation of copper atoms (using Cu (II) acetylacetonate as Cu source) into dicyandiamide-based supramolecular precursor via mechano-chemical reaction, and the Cu atoms and the N atoms are bonded together in two ways: between one Cu atom and four coordinated N atoms (that comes from adjacent carbon nitride layers) and between one central Cu atom and the three N atoms from identical carbon nitride layer forming an in-plane system. Enhanced ferromagnetism of black Cu-g-C 3 N 4 nanosheets is found for the first time, opening the way to deepen the understanding of the material in novel undiscovered applications and to generate fundamental knowledge of ferromagnetism of Cu incorporated g-C 3 N 4 composite material. This black Cu-g-C 3 N 4 nanosheets composite reveals enhanced visible-light-responsive photocatalytic hydrogen generation (526 μmolg-1h−1) as well as excellent CO (5.0 μmolg-1h−1) and CH 4 generation (2.4 μmolg-1h−1) efficiency. Moreover, outstanding conversion rate (90.4 %) and high selectivity to phenol (99.1 %) are obtained in visible-light-driven benzene oxidation application. [ABSTRACT FROM AUTHOR]

Abstract: Nano-structured Pd infiltrated and Pd0.95M0.05 (M = Mn, Co, Ce, and Gd) co-infiltrated Y2O3–ZrO2 (YSZ) electrodes are studied as the oxygen electrodes of solid oxide electrolysis cells (SOECs). The infiltrated Pd-YSZ electrodes show good electrocatalytic activity for the oxygen evolution reaction. For example, the electrode polarization resistance (R E) for 2.0 mg cm−2 Pd infiltrated YSZ is 0.36 Ω cm−2 at 800 °C. R E is not significantly affected by co-infiltrating Pd with Mn and Co, but is enhanced by co-infiltration of Ce and Gd. The co-infiltration of low concentrations of metals in particular Co, Ce and Gd significantly enhances the microstructure and performance stability of the Pd-YSZ electrodes. The results demonstrate that the addition of dopants to the Pd in the form of either an alloy (Co) or a separate phase (Ce and Gd) is beneficial to enhance the performance and stability of Pd based oxygen electrodes of SOECs. [Copyright &y& Elsevier]

Abstract: The impact of volatile boron species on the microstructure and performance of nano-structured (Gd,Ce)O2-infiltrated (La,Sr)MnO3 (GDC-LSM) cathodes of solid oxide fuel cells is studied for the first time. The results indicate that after the heat treatment of the cathodes at 800°C in air for 30days in the presence of borosilicate glass significant grain growth and agglomeration of infiltrated GDC nanoparticles are observed. The electrode polarization resistance of the GDC–LSM cathode after the heat treatment in the presence of glass is 3.15Ωcm2 at 800°C, substantially higher than 0.17Ωcm2 of the cathode heat-treated in the absence of glass under identical conditions. ICP-OES analysis shows the deposition of boron species in the cathodes after sintering in the presence of glass powder. The results demonstrate the significant detrimental effect of volatile boron species on the microstructure and activity of nano-structured GDC–LSM cathode. [Copyright &y& Elsevier]

Abstract: The effect of co-infiltration of Co2MnO4 (CM) spinel oxides and Pd on the electrochemical activity and microstructure stability of La0.7Ca0.3Cr0.5Mn0.5O3−δ (LCCM) cathodes for the O2 reduction reaction of intermediate temperature solid oxide fuel cells (IT-SOFCs) has been investigated in detail. The microstructure, thermal stability, electrochemical activity and stability of the Co2MnO4–Pd/PdO powders and Co2MnO4–Pd/PdO co-impregnated LCCM cathode were measured using thermal gravimetric analysis, X-ray diffraction, scanning electron microscopy and electrochemical impedance spectroscopy. The results indicate that the addition of spinel oxides effectively inhibits the growth and coalescence of the Pd/PdO nanoparticles and stabilizes the microstructure of the Pd/PdO at high temperatures. The best electrochemical activity and stability of LCCM cathodes were obtained on the cathode co-infiltrated with 50wt% PdO/50wt% Co2MnO4. The enhancement is due to the significantly improved stability of the microstructure as a result of the inhibited grain growth and agglomeration of Pd/PdO nanoparticles by the co-infiltrated Co2MnO4 spinel phase. [Copyright &y& Elsevier]

Abstract: Nano-structured Pd x Pt1−x (x =0–1) composite catalysts supported on Ti substrate are successfully prepared by electrodeposition method, and the morphology and phase of the catalysts are analyzed by field emission scanning electron microscope (FE-SEM) and X-ray energy dispersion spectroscopy (EDS). The activity and stability of the Pd x Pt1−x /Ti composite catalysts are assessed for the electrooxidation of alcohols (methanol, ethanol and 2-propanol) in alkaline medium using cyclic voltammetry and chronoamperometry techniques. The results show that the Pd and Pt form Pd x Pt1−x nano-structured composite catalysts, uniformly distributed on the Ti substrate. The electrocatalytic activity and stability of the Pd x Pt1−x nanocatalysts depend strongly on the atomic ratios of Pd and Pt. Among the synthesized catalysts, the Pd0.8Pt0.2/Ti displays the best catalytic activity and stability for the electrooxidation reaction of alcohols investigated in alkaline medium under conditions in this study, and shows the potential as electrocatalysts for direct alcohol fuel cells. [Copyright &y& Elsevier]

• N, S co-doped graphene nanosheets were obtained via a one-step solid reaction method. • The specific N species in carbon matrix can be controlled. • The synergy of S and various N types determine selectivity for ORR or/and OER. The precise regulation of N, S doping and their synergetic effect is essential for N, S co-doped carbon materials as efficient metal-free electrocatalysts for oxygen redox reaction (Oxygen reduction reaction (ORR) and Oxygen evolution reaction (OER)). Herein, an effective precursor modulated active sites engineering strategy of N, S co-doped graphene nanosheets (NSG) were developed by one step pyrolysis of 5-aminouracil (ANA) as N-containing precursor, ammonium persulfate (AP) and 2, 5-dithiobiurea (DBA) as S source, respectively. The results indicate that the specific N doping species in NSG and their synergetic effect with S dopants is strongly dependent on the S sources, which induces huge divergence of electrocatalytic activity and selectivity of NSG nanosheets for ORR and OER. The NSG prepared by ANA and AP as precursors with dominant graphitic N dopant coordinated with S possess the best ORR performance with half-wave potential, E 1/2 of 0.87 V vs. RHE in 0.1 M KOH and poor OER performance with a high potential of 1.67 V at 10.0 mA cm−2, E j=10. On the other hand NSG derived from ANA and DBA with dominant pyridinic N and pyrrolic N dopants exhibits the highest bifunctional activity for both OER and ORR with ΔE (ΔE = E j=10 -E 1/2) of 0.73 V and the performance has been verified on a rechargeable Zn-Air battery fabricated by NSG with a peak power density of 146 mW·cm−2, specific capacity of 796 mAh·g Zn −1, higher than that with state-of-the art Pt/C and IrO 2 (1:1 wt%) air electrode at the same catalyst loading. These excellent performance fundamentally originates from the optimized intermediates energy of ORR or/and OER via the constructed configuration of S and different N species in graphene nanosheets prepared by the specific N and S precursors. The dependence of electrocatalytic selectivity and activity for ORR or/and OER on different N, S configurations revealed in this study provides a facile strategy to achieve specific active sites configurations for developing bifunctional metal-free electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • N, S co-doped graphene nanosheets (NSG) were synthesized via a bottom-up strategy. • All NSG are characterized by high surface area and highly graphitization degree. • The ratio of graphitic N and thiophenic S dopants in NSG affects their selectivity. • The optimized NSG exhibit efficient activity and stability for ORR, OER and HER. • The work provides a new insight on engineering active site of doped carbon materials. Precisely tuning synergetic effect between multi-heteroatom dopants in carbon matrix for water-cycled reactions such as hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is critical for fuel cell and water splitting technologies. Herein, an effective active sites engineering strategy of bottom-up synthesized N, S co-doped graphene (NSG) nanosheets was developed via a facile pyrolysis of the mixed solid power of 2,6-diaminopyridine (DAP) as N source and ammonium persulfate (AP) as S source. All NSG nanosheets prepared with various mass ratio of DAP and AP possess high surface area up to more than 1000 m2 g−1 and highly degree of crystallinity, but display significant differentiation in electrocatalytic selectivity, in which, the NSG prepared by DAP and AP with the mass ratio of 1:1 displays the highest ORR performance with a half-wave potential of 0.87 V vs. RHE, while the NSG with the mass ratio of 3:1 and 1:3 exhibit the highest activity for OER and HER respectively, achieving the corresponding potential of 1.58 V vs. RHE and 0.118 V vs. RHE at 10 mA cm−2, respectively. These activities are comparable and even better than their precious metal counterparts, outperforming the vast majority of reported doped carbon materials prepared using other strategies and precursors. The excellent eletrocatalytic activity and selectivity essentially originate from the optimized intermediates energy of three-reaction pathways via active sites engineering constructed by tuning the ratio of graphitic-N and thiophenic-S dopants in NSG nanosheets, obtained by controlling the ratio of precursors of DAP and AP. This tuning strategy of active sites provides an effective and convenient way to develop precisely function-orientated water-cycled electrocatalysts based on a certain platform of N-containing precursor. [ABSTRACT FROM AUTHOR]