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In an attempt to explore high efficient and cheap electrocatalyst for water splitting hydrogen production, small molybdenum carbide nanoparticles with the size about 3–6 nm are loaded on three-dimensional N-doped carbon matrix successfully with ammonium heptamolybdate ((NH 4 ) 6 Mo 7 O 24 ·4H 2 O) and filter paper as precursor by pyrolysis. Due to its small size, large surface area and high conductivity, this electrocatalyst shows excellent activity in hydrogen evolution reaction (HER). In acid media, its overpotential to achieve a current density of 10 mA·cm −2 is as low as 167 mV, with Tafel slope is only 73 mV·dec −1 . The electrocatalyst also shows large exchange current density (j 0 ) with the value 0.15 mA·cm −2 . Furthermore, it shows excellent durability after 1000 cycles of long-term test, and the catalytic current remains stable over 10 h at fixed overpotential. This work elucidates a feasible strategy to obtain efficient electrocatalysts with cheap and naturally sustainable material as precursor and shed some light on the exploration and optimization of electrocatalysts in energy chemistry. The HER of this electrocatalyst is studied and the results illustrate it exhibits a stable hydrogen evolution rate of 44.5 μmol·h −1 with faradaic efficiency about 100%. [ABSTRACT FROM AUTHOR]

Designing highly efficient electrocatalysts for oxygen evolution reaction is important to meet the requirement of various renewable energy storage and conversion devices. Generally, the performance of OER catalysts can be significantly improved by synergistic action of the underlying conductive substrate. In this work, a commercial graphite paper was used as a facile substrate with catalytic activity. Graphite paper produced 10 mA cm −2 at an overpotential of 447 mV with a Tafel slope of 62 mV dec −1 . By depositing NiFe hydroxide or Mn oxide film onto the graphite paper, the electrode presented a superior activity for water oxidation, which was believed to be synergistically contributed by their available electrochemically active sites associated with the deposited film and the active substrate. High activities were also accompanied by remarkable durability at large current density levels. Our results illustrated a guideline to the design of inexpensive and highly active composite electrode for water oxidation. [ABSTRACT FROM AUTHOR]

Dealloyed Cu@Pt core-shell electrocatalyst was fabricated by cyclic co-electrodeposition and selective Cu dealloying (CCEd-sCuD) on carbon paper (CP), namely Cu@Pt/CP. The Cu@Pt/CP exhibited a core-shell structure comprising with a Cu-rich core and a Pt-rich shell. The crystalline phases of Pt/CP and Cu@Pt/CP were a face-centered cubic (fcc). The compressive lattice strain approximately 0.85% was found in the Cu@Pt/CP owing to a lattice mismatch between a core and a shell region. In the core-region, Cu was formed Pt-Cu alloy as major and copper oxide and also metallic copper as minor. The morphology and grain size of the Cu@Pt/CP displayed a porous spherical shape with 100 nm in diameter, while those of Pt/CP seemed to be a cubic shape with smaller diameter of 40 nm. In electrochemical and catalytic activity, the surface of Cu@Pt/CP had a larger electrochemical active surface area (ECSA) than that of Pt/CP due to a porous formation caused by Cu dealloying. It is not surprising that the Cu@Pt/CP showed higher catalytic activity and greater stability towards 0.5 M 2-propanol electrooxidation in 0.5 M H 2 SO 4 in terms of peak current density (j p ), peak potential (E p ), onset potential (E onset ), diffusion coefficient ( D ), and charge transfer resistance (R ct ) which were caused by electronic structure modification, higher compressive lattice strain, and larger ECSA, compared with Pt/CP. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lamellar structured Ce-S-NC was synthesized with the sheet thickness of 2–3 nm. • Ce-S-NC was applied as the cathode catalyst in alkaline DMFC and DBFC. • Ce-S-NC cathode catalyst shows excellent durability at high current density. • Ce-S-NC are beneficial to improve mass transfer at cathode. Passive direct liquid fuel cells are promising power generation devices with the advantages of convenient transportation, storage for liquid fuel and high power density. This paper focuses on improving the intrinsic electrocatalytic performance and durability of nitrogen-doped carbon (N-C) cathodic electrocatalysts. Then, lamellar structured Ce-S-NC heterogeneous electrocatalyst was synthesized and used as a highly durable cathode for two types of passive direct liquid fuel cells, i.e. , direct methanol fuel cells (DMFCs) and direct borohydride fuel cells (DBFCs). In this work, the effect of the S/C molar ratio on the microstructure and electrocatalytic performance of the Ce-S-NC electrocatalysts was investigated, and excellent intrinsic oxygen reduction reaction activity was obtained at an S/C molar ratio of 0.15. The peak power densities of Ce-S-NC based DMFCs reached up to 12.5, 23.6 and 41.9 mW·cm−2 at 20, 40 and 60 °C, respectively. The peak power densities of 59.3, 84.6 and 132.6 mW·cm−2 were obtained in Ce-S-NC based DBFCs at 20, 40 and 60 °C, respectively. In the durability tests, both the Ce-S-NC based air-breathing DBFCs and passive DBFCs showed the stable operation than that of N-C and Ce-NC. When the current density increased from 50 to 150 mA·cm−2, the Ce-S-NC based DBFC can be operated for 882 h, and only 34 and 91 h for that of N-C and Ce-NC. The electrochemical impedance spectroscopy tests proved Ce-S-NC based DBFC showed the faster mass transfer efficiency. The outstanding durability of Ce-S-NC is mainly attributed to the improved defect density and mass transfer. [ABSTRACT FROM AUTHOR]

Water dissociation reaction (Volmer step) is the main restrictive factor that gives rise to the sluggish reaction kinetics for hydrogen evolution reaction (HER) in alkaline solution. In this paper, Ru doped Ni(OH) 2 deposited on Ti mesh (abbreviated as TM) was synthesized by one-pot hydrothermal method. SEM, TEM, XRD, Raman, and XPS analysis indicated that both surface morphology and electronic structure had an apparent change, but phase structure maintained unchanged after Ru doping. HER activities of Ru doped Ni(OH) 2 /TM samples in 1.0 M KOH were investigated in detail. Ru doped Ni(OH) 2 /TM prepared with 0.2 mM RuCl 3 precursor (denoted as Ru doped Ni(OH) 2 /TM-0.2) presented excellent HER performance with an overpotential of 135 mV at −10 mA/cm2 and the lowest Tafel slope of 63.7 mV/dec. This electrocatalyst also maintained long-term stability even operating for 15 h. Experimental results demonstrated that Ru doping into Ni(OH) 2 could enhance charge transfer rate, increase electrocatalytically active surface area (ECSA) and, most importantly, accelerate Volmer step and also provide appropriate Ru active sites for hydrogen adsorption, which endowed Ru doped Ni(OH) 2 /TM-0.2 with superior HER activity and durability. Unlabelled Image • Ru doped Ni(OH) 2 on Ti mesh was synthesized by one-pot hydrothermal method. • Ru doping greatly enhanced alkaline HER performance with 135 mV at −10 mA/cm2. • Synergistic effect between Ru and Ni in Ru doped Ni(OH) 2 promoted HER kinetics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Four diverse morphologies NiCo 2 S 4 on nickel foam were synthesized; • Caterpillar-like NiCo 2 S 4 consists of 1D nanoneedles and 2D nanosheets; • Caterpillar-like NiCo 2 S 4 demonstrates superior OER activity; • Caterpillar-like NiCo 2 S 4 presents excellent stability. Abstract Design of highly efficient, stable and low-cost water oxidation electrocatalysts continues to be a great impetus and significant challenge for renewable energy systems. In this paper, four diverse morphologies of NiCo 2 S 4 including one-dimensional nanoneedles, two-dimensional nanosheets, three-dimensional flower-like and caterpillar-like arrays are direct grown on nickel foam via a facile two-step hydrothermal process. Influences of synthesis conditions on forming process, morphology, constitution and properties are discussed in detail. Results show that caterpillar-like NiCo 2 S 4 catalyst displays the best electrocatalytic activity toward oxygen evolution reaction, which only needs an overpotential of 279 mV to deliver a current density of 50 mA·cm−2 and the Tafel slope is 68 mV/dec in 1 M KOH. Furthermore, caterpillar-like NiCo 2 S 4 demonstrates excellent stability with inappreciable change of current density after 20 h of oxygen release. This work provides a wide range of possibilities for the further development of cost-effective high efficient electrocatalyst towards oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Highlights • Ru@Pt/C-TiO 2 was prepared by physical mixture and two-step ethanol reduction method. • Ru@Pt/C-TiO 2 exhibited superior MOR activity and enhanced CO tolerance. • The enhanced MOR performance was due to bifunctional mechanism and electronic effect. Abstract Efficient removal of CO species binding with Pt active sites during methanol oxidation reaction (MOR) is vital for an excellent electrocatalyst. In this paper, well-controlled Ru@Pt/C-TiO 2 with much weakened CO adsorption was prepared as MOR electrocatalyst. The nanostructure shows enhanced electroactivity in MOR with peak current density of 1.08 mA/cm2, significantly larger than that of Ru@Pt/C (0.76 mA/cm2), Pt/C-TiO 2 (0.66 mA/cm2) and Pt/C (0.34 mA/cm2). The stability and CO tolerance of Ru@Pt/C-TiO 2 are also superior to that of Ru@Pt/C, Pt/C-TiO 2 and Pt/C. This enhanced MOR performance is ascribed to bifunctional mechanism derived from TiO 2 and strong electronic interaction between Pt and Ru, C-TiO 2 , weakening binding energy of CO adsorbed on Pt. [ABSTRACT FROM AUTHOR]

[Display omitted] • MnCo 2 O 4 /CNT with different exposed facets was synthesized. • Exposure of spinel on different surfaces greatly affected ORR activity. • The ORR half-wave potential of MnCo 2 O 4 /CNT-800 is 0.79 V. • MnCo 2 O 4 /CNT catalyst exhibited higher stability than Pt/C. • The ORR active sites were determined by DFT calculation. Understanding the mechanism of the four-electron transfer oxygen reduction reaction (ORR) and the structure–activity relationship of spinel oxide remains a challenge. Two bimetallic manganese-cobalt spinel oxide supported on carbon nanotube (MnCo 2 O 4 /CNT) composite materials with different crystal planes exposed are synthesized in this paper by adding unequal amounts of ammonia during the hydrothermal process. Physical characterization results indicate that the exposed surfaces of the two materials (MnCo 2 O 4 /CNT-100, MnCo 2 O 4 /CNT-800) are (0 0 1) and (1 1 2), respectively. Electrochemical tests demonstrate that the MnCo 2 O 4 /CNT-800 composite material exposed to the (1 1 2) crystal plane exhibit higher ORR catalytic activity in alkaline electrolyte, with a half-wave potential of 0.79 V and a limiting current density of 5.15 mA cm−2. The outstanding activity is attributed to the greater specific surface area, the exposure of high-index crystal plane and the high-valence metal sites on the surface. Density functional theory (DFT) calculations reveal that the active sites on the (1 1 2) crystal plane have improved adsorption and ORR thermodynamics. This work provides a strategy for developing the advanced bimetallic spinel electrocatalysts by adjusting the exposed plane. [ABSTRACT FROM AUTHOR]

The importance of stabilizing ligands cannot be understated for the colloidal synthesis of nanoparticles as well as their dispersion and assembly into macro-structures such as electrodes. We have recently demonstrated a novel all-inorganic ligand approach to Pt nanoparticle synthesis where surface-adsorbed Sn serves as both reducing agent and stabilizing ligand, producing remarkably monodispersed nanoparticles. By eliminating the need to remove organic surfactants prior to nanoparticle incorporation into electrodes, we were able to use electrostatic assembly to achieve well-defined nanoparticle dispersions in contrast to the aggregated structures common in the field. The approach has allowed us to elucidate the nature of structure sensitivity for electrocatalytic oxygen reduction reaction in acidic and alkaline media. In this paper, we provide a detailed investigation of the evolution of surface-adsorbed Sn-Pt ligand interaction during Pt nanoparticle growth. We show that surface adsorbed SnCl 3 − exists as pyramidally coordinated to the Pt nanoparticle through Sn-Pt bond formation, resulting in a distorted tetrahedrally coordinated Sn-moiety. Furthermore, we show the shift in the bond charge distribution as the Pt is reduced from its initial Pt 2+ state to its metallic state. Direct evidence for the distorted tetrahedral coordination of Pt-SnCl 3 − and the shift in Sn-Pt bond charge during nanoparticle growth emerges from the 119 Sn Mossbauer quadrupole splitting (QS) and Isomer-shift (IS) respectively. Evolution of the structure and chemistry of inorganic complexes during nanoparticle growth has never before been demonstrated and our work is the first to identify the strength of the Sn-Pt interaction in these systems. Such an understanding of nanoparticle surface chemistry will permit extension of this technique to other metals and macro-structures. [ABSTRACT FROM AUTHOR]

Efficient electrocatalytic water splitting is one of the most effective ways to solve the global energy crisis. In this paper, we report on a novel self-assembled hierarchical structure of Co 3 O 4 /CoMoO 4 grown in situ on a bare nickel foam. The unique, three-dimensional honeycomb-like Co 3 O 4 pores were constructed from one-dimensional nanowires and coated on two-dimensional CoMoO 4 nanosheets structures grown on nickel foam. The synthesis involved a step-wise solvothermal method followed by an annealing treatment. Benefiting from the synergistic effect of the hierarchical nanostructures, the materials had more reaction active sites and a smaller electron transfer impedance, and they exhibited excellent electrocatalytic performances for the HER and OER of 143 and 244 mV, respectively, at 10 mA cm −2 in an alkaline solution. Furthermore, the materials remained stable during the long electrolysis period, over 10 h, presenting promising application prospects in the field of electrocatalytic water splitting. [ABSTRACT FROM AUTHOR]

[Display omitted] • The bifunctional catalytic mechanism of LaN x C 4-x -Gra for ORR and OER in acidic and alkaline environments was discussed for the first time. • OH modification is helpful to the improvement of catalytic activity for ORR, but adverse for OER. • LaN 2 C 2 hex-Gra exhibits potential bifunctional activity in alkaline environment and also shows excellent OER activity in acidic environment. • The descriptor f-band center was introduced to rapidly predict catalytic activity. The oxygen reduction/evolution reaction (ORR/OER) on oxygen electrode are the definitive reactions in charge/discharge process of fuel cells and metal air batteries. The research of bifunctional and acidic-alkaline omnipotent electrocatalysts for the oxygen electrode reaction is of great significance for the development and application of electrochemical storage and conversion technologies. In this paper, the catalytic performance of the rare earth LaN x C 4-x -doped graphene (LaN x C 4-x -Gra) catalysts has been discussed extensively. The results demonstrate that in the alkaline environment, LaN 2 C 2 hex-Gra exhibits potential bifunctional activity with the original ηOER is 0.68 V, and the ηORR is 0.56 V accompanied by OH ligands modified. Impressive, LaN 2 C 2 hex-Gra also shows excellent OER activity in acidic environment with the η of 0.68 V. Finally, the catalytic activity can be rapidly evaluated by scale relationship with the introduced band center, which will provide guidance for the development of efficient rare earth single atomic catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Highly porous pyrochlore oxide was synthesized by controlling the temperature of sol–gel process. • Ru nanoparticle anchored on YRO pyrochlore was synthesized by simple In situ exsolution. • Metal-support structure with ultrasmall Ru nanoparticle enhances OER catalytic activity. • Introduction of P dopant changes the electronic structure around metal atoms, enhancing catalytic activity. To enhance green energy technologies, such as metal–air batteries, designing a highly efficient electrocatalyst for the oxygen evolution reaction is crucial because of its sluggish kinetics. In this study, pyrochlore oxide was uniquely synthesized with ultrasmall Ru nanoparticles, a highly porous structure, and a P dopant via simple in situ exsolution, resulting in an outstanding intrinsic activity and surface area. The porous structure of pure pyrochlore was optimized by controlling the temperature of the cross-linking process. The pyrochlore cross-linked at 80 ℃ (YRO-80) had the highest Brunauer-emmett-Teller (BET) surface area (186.1 m2/g). Ultrasmall Ru nanoparticles anchored on Y 2 R 2 O 7 pyrochlore with the P dopant (Ru/YRO-P) were simply synthesized using a one-step process. The high electrocatalytic performance of Ru/YRO-P was demonstrated by its low overpotential (232 mA/cm2), low Tafel slope (41 mV/dec), and high power density (179.2 mW/cm2) in Zn–air battery applications. This paper presents a rational design strategy for enhanced electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • HER performance of vacancy and TM-doped MoSiGeN 4 are fully investigated. • The ΔG H* of V N2 @MoSiGeN 4 and V N1 @MoSiGeN 4 is 0.015 eV and 0.145 eV. • The ΔG H* of Fe-, Mn-, and Nb-doped MoSiGeN 4 is 0.013 eV, 0.061 eV, and 0.087 eV. • Defect engineered Janus MoSiGeN 4 can be served as an efficient HER catalyst. It is well known that defect engineering is very important to the improvement of catalyst activity. In this paper, defect engineering is introduced into Janus MoSiGeN 4 to regulate hydrogen evolution reaction (HER) activity. Based on density functional theory, a theoretical study is carried out to clarify the roles of vacancy and transition metal (TM) atom doping in Janus MoSiGeN 4. Five different vacancies are considered, and results suggest that outmost N vacancy can effectively enhance the HER activities. For V N2 @MoSiGeN 4 and V N1 @MoSiGeN 4 structures, the hydrogen adsorption Gibbs free energy (ΔG H*) is 0.015 eV and 0.145 eV, respectively. Moreover, a systematic screening of eleven non-precious TM atoms (V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Ta and W) doped MoSiGeN 4 as HER catalysts reveals that Fe-, Mn-, and Nb-doped MoSiGeN 4 show better HER activity than that of Pt with theΔG H* of 0.013 eV, 0.061 eV, and 0.087 eV, respectively. Electronic properties, electron charge density difference and Bader charge are employed to explore the origin of electrocatalytic activity. Our study confirms that vacancy and TM atom doping are effective means to enhance electrocatalytic performance and defect engineered Janus MoSiGeN 4 can be served as highly efficient HER catalyst. [ABSTRACT FROM AUTHOR]

A new class of single/several-layer conductive Langmuir-Blodgett MOF films were prepared for ultralow concentration H 2 O 2 detection, creating a new record of H 2 O 2 detection limit based on non-precious catalysts (10−10, m/m). • A simple and scalable method to prepare conductive metal-organic LB films. • A new record of H 2 O 2 detection limit based on the non-precious LB films (10−10, m/m). • Quick response, good sensitivity, high stability, and perfect reproducibility. • Reaction mechanism and electron transfer processes at the internal interfaces. The detection of low-concentration hydrogen peroxide (H 2 O 2) has important theoretical-significance and practical value in many fields, such as medical science, biological chemistry, and food safety inspection. Traditional commercial H 2 O 2 test paper and detection technology can only reach the detection limit of 10−3–10−5 (mass fraction). In this paper, we report a simple method to prepare 2D MOF (metal-organic frameworks) [Co 3 (HOB) 2 ] n films based on Langmuir-Blodgett (LB) method combined with layer-by-layer growth technique. Even 3-layer [Co 3 (HOB) 2 ] n films can realize the lowest H 2 O 2 detection limit of 1.05 × 10−8 wt% (3.08 nmol·L−1) based on the resultant 2D MOF catalyst. Meanwhile, density functional theory (DFT) calculations revealed that Co2+ ions of the LB films decreased the energy of [HOOH] transforming into [HO 2 ] during the H 2 O 2 reduction reactions, thus speeding up the decomposition of H 2 O 2. [ABSTRACT FROM AUTHOR]

Low-crystalline or amorphous molybdenum sulfides (MoS x ), bearing abundant unsaturated active sites, have been identified as efficient catalysts for electrocatalytic and photocatalytic H 2 evolution reactions, however, their intrinsic activity is still low and need to be further improved for large-scale applications. In this paper, we report that low-crystalline MoS x doped with Co (Co-MoS x ) as efficient cocatalysts could be loaded on CdS nanoparticles through a facile and controllable photochemical reduction method and showed high performances in catalyzing H 2 evolution under visible light irradiation (≥420 nm). The photochemical loading of Co-MoS x was accomplished by using an in-situ formed molecular complex precursor and photogenerated electrons on CdS as reductants under mild conditions. The optimized CdS/Co-MoS x (Co:Mo = 1:4, 2 mol% loading) photocatalyst exhibited a catalytic H 2 evolution rate of 535 μmol h −1 , which is 1.8 times higher than that of CdS/MoS x , and an apparent quantum efficiency (AQE) of 23.5% was achieved over CdS/Co-MoS x photocatalyst at 420 nm. Co-MoS x catalyst also shows a long-term stability without noticeable activity degradation. Notably, Co-MoS x cocatalyst was found more efficient than that of noble metals in catalyzing photocatalytic H 2 evolution on CdS. The formation of CoMoS phase, the enhanced electrocatalytic activity as well as reduced electron transfer resistance due to the doping effects of Co ions, account for the enhanced catalytic activity of this Co-MoS x cocatalyst. [ABSTRACT FROM AUTHOR]

The exploration of a metal-free catalyst with highly efficient yet low-cost for the oxygen-reduction reaction (ORR) is under wide spread investigation. In this paper, by using dimethyl sulfoxide (DMSO) as S source as well as solvent, we report a new, low-cost, and facile solvothermal route to synthesize S-doped reduced graphene oxide (S-RGO). The existence of S element in the framework of RGO was solidly confirmed by energy-dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS). The as-synthesized S-RGO can be worked as an efficient metal-free electrocatalyst for ORR. Moreover, compared to commercial Pt/C electrocatalyst, the S-RGO displays superior resistance to crossover effect and stability by evaluating the addition of methanol and CO poisoning experiment. This result not only shows S-RGO as a promising candidate instead of Pt-based catalyst for ORR, but also provides a new approach for the preparation of metal-free electrocatalyst in future. [ABSTRACT FROM AUTHOR]

In this paper, carbon nanotubes (CNTs) was activated by KOH treatment at high temperature and investigated as catalyst for VO 2+ /VO 2 + redox reaction for vanadium redox flow battery (VRFB). X-ray photoelectron spectroscopy results suggest that the oxygen-containing groups can be introduced on CNTs by KOH activation. The mass transfer of vanadium ions can be accelerated by chemical etching by KOH activation and improved wettability due to the introduction of hydrophilic groups. The electrochemical properties of VO 2+ /VO 2 + redox reaction can be enhanced by introduced oxygen-containing groups as active sites. The sample treated at 900 °C with KOH/CNTs mass ratio of 3:1 (CNTs-3) exhibits the highest electrocatalytic activity for VO 2+ /VO 2 + redox reaction. The cell using CNTs-3 as positive catalyst demonstrates the smallest electrochemical polarization, the highest capacity and efficiency among the samples. Using KOH-activated CNTs-3 can increase the average energy efficiency of the cell by 4.4%. This work suggests that KOH-activated CNTs is a low-cost, efficient and promising catalyst for VO 2+ /VO 2 + redox reaction for VRFB system. [ABSTRACT FROM AUTHOR]

Electrochemical reduction of carbon dioxide (CO 2 ) to formate is energetically inefficient because high overpotential is required for reduction of CO 2 to formate on most traditional catalysts. In this paper, a novel nano-sized Bi-based electrocatalyst deposited on a Cu foil has been synthesized, which can be used as a cathode for electrochemical reduction of CO 2 to formate with a low overpotential (0.69 V) and a high selectivity (91.3%). The electrocatalyst can show excellent catalytic performance toward reduction of CO 2 which can probably be attributed to the nano-sized structure and the surface oxide layer. The energy efficiency for reduction of CO 2 to formate can reach to 50% when an Ir x Sn y Ru z O 2 /Ti electrode is used as anode, it is one of the highest values found in the literatures and very practicable for sustainable fuel synthesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Firstly calculated HER & OER activity of anti-perovskites Ni 3 ZnC, Co 3 ZnC and Ni 3 FeN. • HER catalytic performance ranking: Ni 3 ZnC (1 0 0) > Ni 3 FeN (1 1 1) > Co 3 ZnC (1 0 0) • Combining OER and HER performance, Ni 3 ZnC (1 0 0) has the best bifunctional activity. • Experimentally common carbon vacancies are detrimental to HER performance of Ni 3 ZnC. • Doping of Fe for Co 3 ZnC and Cu for Ni 3 FeN may enhance bicatalytic activity. Low-cost anti-perovskites (X 3 AB) as efficient bifunctional electrocatalysts for water splitting have been reported recently. However, its microscopic catalytic mechanism is not clear. In this paper, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance of three typical bifunctional anti-perovskite catalysts Ni 3 ZnC, Co 3 ZnC and Ni 3 FeN were calculated for the first time. Comprehensive analysis reveals that HER catalytic performance ranking: Ni 3 ZnC (1 0 0) > Ni 3 FeN (1 1 1) > Co 3 ZnC (1 0 0). Combined with the OER catalytic activity, we concluded that Ni 3 ZnC (1 0 0) may have the best bifunctional performance. We also calculated the transition-metal doping effect and concluded that the doping of Fe for Co 3 ZnC and Cu for Ni 3 FeN may further enhance the bifunctional catalytic activity. The effect of experimentally common carbon vacancies was calculated to be detrimental to the HER performance. Our work gave an atomic perspective of HER and OER catalytic mechanisms of anti-perovskites, which is helpful for the further development of water splitting electrocatalysts. [ABSTRACT FROM AUTHOR]

Highlights: [•] The paper presents alloy effect of Ni and Co on hydrogen evolution reaction (HER). [•] The various material properties of electrodeposited NiCo alloys are demonstrated. [•] Relationship between activities and material properties are discussed. [•] High activity of HER in alkaline solution is achieved with NiCo alloy catalysts. [ABSTRACT FROM AUTHOR]

Abstract: A novel hybrid system has been investigated based on polyaniline/carbon nanofiber (Pani/CNF) electrospun nanofibers for modification of gas diffusion electrode (GDE) in proton exchange membrane fuel cells (PEMFC). Pani/CNF hybrid nanofibers were synthesized directly on carbon paper by electrospinning method. For preparation of catalyst ink, 20wt.% Pt/C electrocatalyst with a platinum loading of 0.4mgcm−2 was prepared by polyol technique. SEM studies applied for morphological study of the modified GDE with hybrid nanofibers. This technique indicated that the electrospun nanofibers had a diameter of roughly 100nm. XRD patterns also showed that the average size of Pt nanoparticles was about 2nm. Subsequently, comparison of the hybrid electrode electrochemical behavior and 20wt.% Pt/C commercial one was studied by cyclic voltammetry experiment. The electrochemical data indicated that the hybrid electrode exhibited higher current density (about 15mAcm−2) and ESA (160m2 gr−1) than commercial Pt/C with amount of about 10mAcm−2 and 114m2 gr−1, respectively. The results herein demonstrate that Pani/CNF nanofibers can be used as a good alternative electrode material for PEMFCs. [Copyright &y& Elsevier]

[Display omitted] • NiCoP electrocatalyst was prepared by two-step hydrothermal phosphating process. • A simple and controllable method was used to construct layered porous plates to reduce the charge transfer resistance of NiCoP materials and showed the best catalytic performance. • NiCoP porous sheet has a large electrochemical active surface area and catalytic activity and the stability of the catalyst was investigated. Research on the stable and high-efficiency transition metal-based electrocatalyst to achieve hydrogen evolution reaction (HER) becomes one of the core solutions for water decomposition. Non-precious metals phosphide has the potential to become a non-noble metal electrocatalyst due to its good electronic structure effect, extremely low price, and expected durability in a larger pH range. In this paper, hexagonal NiCoP porous nanosheets were synthesized using a facile hydrothermal and post-phosphating method. We anticipate that bimetal doping can further enhance electrocatalyst activity as well as improve the capability of absorbing hydrogen from the materials by modifying the electronic structure. The obtained NiCoP electrocatalyst behaves outstanding catalytic performances for HER in alkaline media with 83 mV initial overpotential at 10 mA cm−2, as well as the low Tafel slopes of 41 mV dec−1. In addition, the current density showed almost no attenuation in the 10 h chronoamperometry experiment. The outstanding catalytic function can be attributed to the nanosheets with many orifices, which can expand the effective reaction specific surface area, promote mass transport and boost the water decomposition efficiency. And the collaboration of Ni and Co in NiCoP nanosheets can also improve the electrochemical function. Moreover, the current work offers a feasible approach for synthesizing a cheap and efficient NiCoP electrocatalyst for HER, which is especially appealing to practical application. [ABSTRACT FROM AUTHOR]

3D HCNs@g-C 3 N 5 heterojunctions composites with built-in electronic filed are synthesized, which are explored as efficient electrocatalyst, showing greatly enhanced ORR activity and long-term durability. [Display omitted] • A facile strategy for the fabrication of 3D HCNs@g-C 3 N 5 heterojunction is synthesized successfully. • HCNs@g-C 3 N 5 heterojunction with built-in electronic field (IEF) boosting active superoxide anion radicals is demonstrated. • Density functional theory is used to untangle the formation mechanism of the IEF. • HCNs@g-C 3 N 5 heterojunction shows enhanced ORR activity and long-term durability. Improving the electrocatalytic activity of metal-free catalysts for the oxygen reduction reaction (ORR) is of great significance as promising alternatives to the Pt group precious catalysts in fuel cells. This paper proposes a simple template-based strategy to fabricate a catalyst with enhanced ORR activity. The resulting material contained 3D heterojunction and consisted of hollow carbon nanospheres and graphitic C 3 N 5 (HCNs@g-C 3 N 5). The fast electron/charge transports between g-C 3 N 5 and HCNs was achieved because of the conductive heterojunction presence. This heterojunction provided the potential difference, which is beneficial for O 2 activation and desorption of the intermediate reaction products. Compared with stand-alone HCNs and g-C 3 N 5 , the HCNs@g-C 3 N 5 composite demonstrated significantly enhanced ORR activity with a more positive half-wave potential and faster kinetics in the alkaline medium. Furthermore, linear sweep voltammetry demonstrated that the water generation from O 2 occurred through a four-electron transfer reaction. According to calculations performed using density functional theory (DFT), a built-in electronic field (IEF) formed at the heterojunction because of the charge density difference between C and N atoms. This IEF reduced the O 2 activation energy and lowered the charge transfer resistance, which, in turn, enabled the rapid formation and desorption of the intermediates and significantly enhanced ORR activity of HCNs@g-C 3 N 5. [ABSTRACT FROM AUTHOR]

• A series of Ru-CoMo/CFP-# (# = 0, 1, 12, 24, 48 h) electrocatalysts were synthesized. • Ru-CoMo/CFP (24 h) demonstrated excellent HER and OER activity. • Ru loading can induce strong electron interactions and endow a better intrinsic activity. Searching for earth-abundant, highly efficient, and stable bifunctional electrocatalysts for water splitting is critical for the further development of sustainable energy generation, yet it remains a great challenge. Herein, a facile electrodeposition strategy followed by wet-chemistry treatment is reported for the fabrication of the ultralow amount loading of ruthenium (Ru) on CoMo alloy supported on carbon fiber paper (CFP) substrate (Ru-CoMo/CFP). Benefiting from the unique nano-architectures and synergetic effect of loading Ru material and CoMo alloy, the optimized Ru-CoMo/CFP exhibits excellent electrocatalytic activity and favourable stability toward electrochemical water splitting. The as-prepared Ru-CoMo/CFP composite exhibits a current density of 10 mA·cm−2 at overpotentials of 44 and 237 mV for catalyzing hydrogen and oxygen evolution reaction (HER/OER) in alkaline medium, respectively. The as-synthetized Ru-CoMo/CFP electrode is also demonstrated to function as anode and cathode, simultaneously, only needs a cell voltage of 1.54 V to yield 10 mA·cm−2, outperforming the state-of-the-art RuO 2 ||Pt/C couple (1.56 V). This work demonstrates substantial improvement in the design of high-efficiency electrodes for water electrolysis. [ABSTRACT FROM AUTHOR]

A novel complex Fe/FeN@N-C nano-electrocatalyst was constructed by adopting a strategy of competitive coordination of nitrogen sources (2-methylimidazole). The competitive coordination of 2-methylimidazole promoted the generation of FeN active sites and greatly improved its ORR electrocatalytic performance. • The electrocatalyst synthesized with MOF as precursor, even distribution of active sites of the electrocatalysts. • Adopt a strategy of competitive coordination to synthesize a novel complex Fe/FeN@N-C electrocatalyst. • 2-methylimidazole promoted the generation of FeN active sites. • 2-methylimidazole acts as both a competitive ligand and a nitrogen source. • Excellent electrocatalytic properties and long-term stability. The development of controllable doping strategies is essential to obtain highly active electrocatalytic materials. Transition metal atoms with corresponding nitrogen coordination have been widely proposed as active centers for electrocatalytic oxygen reduction (ORR) in metal@nitrogen-carbon (M@N-C) electrocatalysts. In this paper, an effective competitive coordination strategy and high-temperature calcination were used to construct a novel complex Fe/FeN@N-C electrocatalyst. The synthesized catalyst, Fe-MIL-101-2-MI, was using 2-methylimidazole as a nitrogen source and a competitive ligand, which affects the nucleation and growth of the crystal. The morphology of the Fe-MIL-101-2-MI is nanorod, which is conducive to electron transport. Moreover, the competitive coordination of 2-methylimidazole promoted the generation of FeN active sites and greatly improved its ORR electrocatalytic performance. A series of Fe/FeN@N-C-X-Ts electrocatalytic samples was synthesized by controlling the doping amount of 2-methylimidazole and different calcining temperatures. Fe/FeN@N-C-2-800 composites exhibit high levels of doped N, even-distribution of Fe nanoparticles, and abundant FeN active sites. It is noteworthy that the half-wave potential of Fe/FeN@N-C-2-800 in the electrocatalytic ORR reaction is 0.813 V (vs. RHE), the initial potential is 0.873 V (vs. RHE), and the limit current density impressively reached 6.04 mA/cm2. In comparison to commercial Pt/C, the synthesized catalyst showed superior electrocatalytic performance. [ABSTRACT FROM AUTHOR]

• The polar nitrobenzene molecule can effectively adjust the electronic structures of g-C 3 N 4. • The most stable composite specimen has OER/ORR overpotentials of 0.27/0.39 V. • The number of active electrons can accurately estimate the OER/ORR activity of metal-free electrocatalysts. Metal-free catalyst with favorable advantages of nonpolluting, cost-effective and stable catalytic performances may be used in various redox reactions. In this paper, we design a series of C 6 H 4 NO 2 /g-C 3 N 4 composites by combining a polar nitrobenzene molecule with g-C 3 N 4 monolayer using density functional theory calculations. The electrocatalytic performances during oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are substantially improved thanks to the electron redistributions of g-C 3 N 4 substrate. One composite specimen exhibits the lowest bi-directional OER/ORR overpotentials of 0.14/0.14 V, and the most stable composite specimen has OER/ORR overpotentials of 0.27/0.39 V. The number of active electrons in active atom, as descriptor of catalytic activity, can accurately estimate the OER and ORR activity of metal-free electrocatalysts. The modification strategy would be extended to design high-efficiency metal-free electrocatalysts. [ABSTRACT FROM AUTHOR]

• The surface of La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 perovskite oxides was modified using diluted HNO 3. • Sr cations on A-sites can be selective dissolved by diluted HNO 3. • Surface area and oxygen vacancies were increased with etching time. • The OER performance was enhanced by selective dissolution of the A-site Sr cations. Perovskite oxide is a potential alternative to precious metal oxides like IrO 2 and RuO 2 as electrocatalysts in the oxygen evolution reaction (OER), mostly for its cost-effectiveness and adequate stability. However, the low catalytic activity in the OER limits its practical application. This paper deals with the preparation of perovskite oxides (by the sol-gel method) with enhanced electrocatalytic activity through selective dissolution of A-site cations of La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 (LSCF) in order to tune the A-site cation deficiency. Additionally, a thorough investigation of the catalysts' OER performance was performed in a 0.1 mol⋅L−1 KOH solution. Based on the results of XRD, SEM, TEM, XPS and ICP-AES, it can be concluded that selective dissolution of Sr cations on A-sites can be achieved using a HNO 3 etching remaining the perovskite structure. The OER catalytic activity of LSCF can be effectively promoted after acid etching for 6 h, which can be attributed to the higher surface area (BET result) and ratio of the high oxidative oxygen species (O2−/O−) and surface oxygen species (OH−/O 2). Moreover, the LSCF catalysts maintains an appropriate electrochemical stability after acid etching. Our work offers a simple but effective way to modify the perovskite surface so as to boost the OER performance. [ABSTRACT FROM AUTHOR]

Four novel morphologies of in-situ grown of MMNS nanostructure arrays (MMNS-NFs1, NFs2, NRs1, and NRs2) were realized and MMNS all behave as an efficient catalyst for electrochemical activities at alkaline condition. The 3D nanorods core-shell nanostructure MMNS-NRs2 exhibits high-efficient electrocatalytic performance towards HER (158 mV @ 10 mA cm−2) and OER (134 mV @ 40 mA cm−2). What's more, when MMNS-NRs2 was served as the bifunctional electrocatalyst for overall water splitting in 1.0 M KOH, only a low cell voltage of 1.52 V and 1.60 V were required for MMNS-NRs2//MMNS-NRs2 electrode pairing to reach the current density 20 mA cm−2 and 100 mA cm−2 and strong long-term electrochemical durability. • 3D nanostructure MMNS with four novel morphologies were fabricated. • MMNS-NRs2 exhibits high-efficient HER and OER performance. • MMNS-NRs2//MMNS-NRs2 exhibits superior performance for overall water splitting. • MMNS-NRs2 nanorods present the unique core-shell nanostructure. • The interfaces accelerate electron/ion transfer and favor reaction kinetics. It is highly desired but still a significant challenge to construct preeminent non-noble metal bifunctional electrocatalysts for large-scale electricity-to-hydrogen generation. In the paper, four novel morphologies of MMNS including epiphyllum-like MMNS-NFs1, ice flower-like NFs2, grape-like NRs1, and nanorod NRs2 were successfully achieved via a facile two-step process by adjusting C 2 H 5 NS/CO(NH 2) 2 M ratio and/or H 2 O/ethanol solvent composition. Electrochemical activities of as-prepared four samples were systematically studied, while 3D nanorods core-shell nanostructure MMNS-NRs2 exhibits high-efficient electrocatalytic performance towards HER (158 mV @ 10 mA cm−2) and OER (134 mV @ 40 mA cm−2). What's more, when MMNS-NRs2 was served as the cathode and anode for overall water splitting in 1.0 M KOH, only a low cell voltage of 1.52 V and 1.60 V were required for MMNS-NRs2//MMNS-NRs2 electrode pairing to reach the current density 20 mA cm−2 and 100 mA cm−2, respectively. MMNS-NRs2//MMNS-NRs2 also performs an outstanding long-term durability at least 16 h without obvious deactivation. The reason for outstanding electrochemical properties and stability of MMNS-NRs2 was owing to the fact that unique core-shell nanostructure can facilitate electron/ion transfer and mass transport, 3D nanosheets endow more active sites and higher electron transport rate and the synergistic effect of Mo and Mn composition. This work provides a well-designed structure and development for morphology engineering to construct high-performance material for clean energy conversion technologies. [ABSTRACT FROM AUTHOR]

The sluggish anodic water oxidation reaction is synergistically activated over fishnet-like superstructures constructed from ultrafine and ultralong Ni-MOF nanowire arrays directionally grown on highly rough and conductive scaffolds. • In water electrolysis, the anodic water oxidation needs much higher overpotential than cathodic water reduction. • The Fishnet-like superstructures constructed from ultrafine and ultralong Ni-MOF nanowire arrays on highly rough and conductive scaffolds can synergistically deliver efficient and robust alkaline water oxidation activity. • A η 10 of 240 mV is maintained after a long-term durability test for as long as 32 h. The water oxidation efficiency driven by electrocatalysts is related to the energy conversion efficiency of water electrolysis and other systems. It is the key to expose active sites as possible, to fully and firmly contact with other components, and to deliver superior conductivity for the development of high-performance electrocatalysts. Herein, we have fabricated self-supporting Ni-MOF electrode containing three-dimensional (3D) fishnet-like superstructures, which are constructed from in-situ growth of amorphous or poor crystalline Ni-MOF nanowire arrays on highly rough and conductive scaffolds of metallic Ni/carbon cloth (Ni-MOF/Ni/CC). The Ni-MOF/Ni/CC electrode delivers an overpotential of 250 mV at the current density of 10 mA cm−2 (η 10). The η 10 is maintained at 240 mV after a constant current electrolysis for 32 h, which is much smaller than those of Ni-MOF/CC (423 mV) and Ni/CC (281 mV). The superior activity and robust durability can be attributed to the synergistic activating effect of each component in the superstructures with high density of coordination unsaturated active sites, intimate connection and excellent conductivity. This work can provide a new strategy to develop high-efficiency MOFs-based electrocatalysts for electrocatalytic water oxidation. [ABSTRACT FROM AUTHOR]