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The development of high‐efficient electrocatalysts with low applied voltage and robust stability is of great importance for electrolysis of water. In this work, a bifunctional electrode has been developed by growing palladium‐modified FeCoS2 nanosheet arrays on Ni foam (Pd‐FeCoS2 NAs/NF), which can serve as anode and cathode for alkaline water splitting with high activities and ultra‐strong durability. The Pd‐FeCoS2 NAs/NF shows overpotentials of 130 mV for hydrogen evolution reaction (HER) and 202 mV for alkaline oxygen evolution reaction (OER) at 10 mA cm−2. The alkaline electrolyzer is built by employing Pd‐FeCoS2 NAs/NF as cathode and anode, delivering a current density of 50 mA cm−2 at 1.59 V. Moreover, the electrolyzer can run stably for 600 h with negligible decline. [ABSTRACT FROM AUTHOR]

Development of low cost electrocatalysts with outstanding catalytic activity and stability for oxygen evolution reaction (OER) in acid is a major challenge to produce hydrogen energy from water splitting. Herein, a novel metal‐free electrocatalyst consisting of a oxygen‐functionalized electrochemically exfoliated graphene (OEEG) nanosheets array is reported. Benefitting from a vertically aligned arrays structure and introducing oxygen functional groups, the metal‐free OEEG nanosheets array exhibits superior electrocatalytic activity and stability toward OER with a low overpotential of 334 mV at 10 mA cm−2 in acidic electrolyte. Such a high OER performance is thus far the best among all previously reported metal‐free carbon‐based materials, and even superior to commercial Ir/C catalysts (420 mV at 10 mA cm−2) in acid. Characterization results and electrochemical measurements identify the COOH species in the OEEG acting as active sites for acidic OER, which is further supported by atomic‐scale scanning transmission electron microscopy imaging and electron energy‐loss spectroscopy. Density functional theory calculations reveal that the reaction pathway of dual sites that is mixed by zigzag and armchair edges (COOH‐zig‐corner) is better than the pathway of single site. [ABSTRACT FROM AUTHOR]

Development of cost‐effective and highly efficient oxygen evolution reaction (OER) electrocatalysts has become a vital project of renewable energy technologies. The OER is critical for a variety of electrochemical energy devices such as water electrolyzers, metal‐air batteries, CO2 reduction, and electrosynthesis of ammonia. Compared to extensively studied metal oxide catalysts, graphitized carbon catalysts have been newly emerged as promising OER catalysts especially in less corrosive alkaline media, due to their low cost, high electrical conductivity, unique physicochemical properties, and excellent electrocatalytic performances. In this review, we discussed recent advances in nanostructured carbon electrocatalysts. At first, metal‐free OER carbon electrocatalysts including single‐ and multi‐heteroatom doping and edge‐ and defect‐rich defects are introduced. Then, transition metal and heteroatom co‐doped nanocarbons are summarized including Co−N−C, Ni−N−C, and Fe‐N−C. In addition, carbon based hybrid electrocatalysts are highlighted, which include carbon based transition metal nitrides (TMNx), sulfides (TMSx), and selenides (TMSex), and phosphides (TMPx). Finally, current challenges and perspective for future research on carbon‐based OER catalysts are outlined. [ABSTRACT FROM AUTHOR]

In an article published in Advanced Functional Materials, researchers Zhenhai Wen, Cheng‐Yan Xu, and their team introduce a low-cost and durable catalyst called Pt@CoN4‐G. This catalyst contains atomic Co and Pt species encapsulated in nitrogen-doped graphene and demonstrates excellent performance in both the hydrogen evolution reaction and the oxygen reduction reaction. The catalyst shows promise for use in flow alkali‐Al/acid hybrid fuel cells and Zn–air batteries. The researchers attribute the catalyst's success to the strong metal support interactions between the Pt species and the CoN4‐G support, as well as the synergistic cooperation of multiple active sites. [Extracted from the article]

It is highly attractive to develop efficient water electrolysis route to implement hydrogen generation in a low‐cost way, which while requires excess energy to surmount the activation barriers majorly limited by oxygen evolution reaction at anode side. Herein, we report an acid‐alkali asymmetric‐electrolyte electrolyzer (AAAE) that can achieve substantial energy saving for electrolysis hydrogen generation, thanks to the assistance of electrochemical neutralization energy (ENE) and urea oxidation reaction (UOR). To this end, free‐standing Ni(OH)2 nanosheets on carbon cloth (Ni(OH)2−NSs/CC) is fabricated as catalytic anode for alkaline UOR, which manifests impressively high catalytic activity with delivering 10 mA cm−2 at 1.32 V and long‐term durability. The as‐developed AAAE only requires an applied voltage of 0.66 V to release the electrolysis current of 10 mA cm−2, yielding the H2 Faraday efficiency close to 100 % along with H2 production rate of 183.8 μmol h−1. [ABSTRACT FROM AUTHOR]

Developing efficient and low‐cost catalysts with excellent catalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of significance for large‐scale commercial applications in rechargeable Zn−air batteries and fuel cells. Herein, we develop a simple, mild and efficient method to synthesize a hybrid of N‐doped carbon nanosheets encapsulating cobalt nanoparticles (Co@NCNSs), which shows favorable catalytic properties toward both ORR and OER with high activity and good stability. The optimized hybrids (Co@NCNSs‐900) exhibit an onset potential of 0.95 V vs. reversible hydrogen electrode (RHE) and a half‐wave potential of 0.85 V vs. RHE for the ORR, and an onset potential of 1.51 V vs. RHE, a potential of 1.59 V vs. RHE at 10 mA cm−2 for the OER, as well as an oxygen electrode activity parameter (ΔE) of 0.802 V in alkaline electrolyte. Moreover, the Zn−air battery with the Co@NCNSs‐900 as the cathode catalyst outperforms that with the commercial Pt/C as cathode catalyst in terms of the maximum power density and stability, showing great prospects in renewable energy applications. [ABSTRACT FROM AUTHOR]

Nanohybrids with hollow CoNiP nanoparticles decorating reduced graphene oxide (h-CoNiP/rGO) are prepared by a low-temperature phosphorization method. The h-CoNiP/rGO present favorable electrocatalytic advantages toward the oxygen evolution reaction (OER) in alkaline solution, including an onset potential of 1.44 V, a low overpotential of 280 mV at a current density of 10 mA cm − 2 , a small Tafel slope of 65.2 mV dec − 1 , and pretty good durability. The use of earth-abundant elements in a high-activity OER electrocatalyst may provide an effective way of advancing the development of full water splitting. [ABSTRACT FROM AUTHOR]

A novel OER electrocatalyst, namely oxygen-incorporated amorphous cobalt sulfide porous nanocubes (A-CoS4.6O0.6 PNCs), show advantages over the benchmark RuO2 catalyst in alkaline/neutral medium. Experiments combining with calculation demonstrate that the desirable O* adsorption energy, associated with the distorted CoS4.6O0.6 octahedron structure and the oxygen doping, contribute synergistically to the outstanding electrocatalytic activity. [ABSTRACT FROM AUTHOR]

A novel hybrid electrocatalyst consisting of nitrogen-doped graphene/cobalt-embedded porous carbon polyhedron (N/Co-doped PCP//NRGO) is prepared through simple pyrolysis of graphene oxide-supported cobalt-based zeolitic imidazolate-frameworks. Remarkable features of the porous carbon structure, N/Co-doping effect, introduction of NRGO, and good contact between N/Co-doped PCP and NRGO result in a high catalytic efficiency. The hybrid shows excellent electrocatalytic activities and kinetics for oxygen reduction reaction in basic media, which compares favorably with those of the Pt/C catalyst, together with superior durability, a four-electron pathway, and excellent methanol tolerance. The hybrid also exhibits superior performance for hydrogen evolution reaction, offering a low onset overpotential of 58 mV and a stable current density of 10 mA cm−2 at 229 mV in acid media, as well as good catalytic performance for oxygen evolution reaction (a small overpotential of 1.66 V for 10 mA cm−2 current density). The dual-active-site mechanism originating from synergic effects between N/Co-doped PCP and NRGO is responsible for the excellent performance of the hybrid. This development offers an attractive catalyst material for large-scale fuel cells and water splitting technologies. [ABSTRACT FROM AUTHOR]

Optimized electrocatalyst that hybrids with carbon coating FeCoP x nanoparticles possesses catalytic activity toward ORR, OER and HER. Furthermore, through the design of alkali-acid electrolyzer and device integration, for the very first time, a single Zinc-air battery enable to drive an alkali-acid electrolyzer for producing hydrogen and oxygen. [Display omitted] • A one-pot scalable pyrolysis strategy to fabricate a tri-functional electrocatalyst. • High catalytic activity toward ORR&OER in alkaline and HER in acidic media. • The Zn-air battery can run stably for 1500 cycles. • An alkali-acid electrolyzer only requires 0.99 V to release an electrolysis current density of 10 mA cm−2. • A single self-made Zinc-air battery can drive an alkali-acid electrolyzer to produce hydrogen. Developing handy synthesis routes to fabricate low-cost, high-activity, and multifunctional electrocatalysts for a variety of electrochemical reactions is highly desirable so as to achieve the goal that one catalyst can be used for integrated electrolysis devices, thus greatly simplifying the electrocatalyst system processing. Here, we report a one-pot scalable pyrolysis strategy to fabricate a tri-functional electrocatalyst, i.e. , hybrids with carbon coating FeCoP x nanoparticles, which shows favorable electrocatalytic properties toward oxygen reduction reaction, oxygen evolution reaction in alkaline solution, and hydrogen evolution reaction in acidic condition. The new synthesis routes enable us to readily develop an integrated device with a Zn-air battery driving an alkali-acid electrolyzer by just using one catalyst. The present work may shed light on the practical viability of the development of multifunctional electrocatalysts for integrated devices applications. [ABSTRACT FROM AUTHOR]

A facile self-templated carbonization strategy is developed for fabrication of a bifunctional electrocatalyst with uniform distribution of F, N heteroatoms, mesoporous channels and abundant edge-defect by direct pyrolysis of F, N -containing covalent organic framework (F-COF) precursor. The designed catalyst exhibits excellent bifunctional catalytic activity with a small OER-ORR potential gap of 0.79 V. The assembled ZAB delivers a high peak density of 206.3 mW cm−2 and good cyclic stability. [Display omitted] • F, N co-doped porous carbon (F-NPC) was facile prepared by in situ pyrolysis of fluoric COF precursor. • Experiments combined with theoretical calculation confirmed the significant contribution of F in boosting the catalytic reactivity. • The designed F-NPC catalyst shows superior ORR and OER activity. • The assembled ZAB using F-NPC catalyst displays high peak power density and excellent durability. The construction of heteroatom-doped metal-free carbon catalysts with bifunctional catalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is highly desired for Zn-air batteries, but remains a great challenge owing to the sluggish kinetics of OER and ORR. Herein, a self-sacrificing template engineering strategy was employed to fabricate fluorine (F), nitrogen (N) co-doped porous carbon (F-NPC) catalyst by direct pyrolysis of F, N containing covalent organic framework (F-COF). The predesigned F and N elements were integrated into the skeletons of COF precursor, thus achieving uniformly distributed heteroatom active sites. The introduction of F is beneficial for the formation of edge-defects, contributing to the enhancement of the electrocatalytic activity. Attributing to the porous feature, abundant defect sites induced by F doping, as well as the strong synergistic effect between N and F atoms to afford a high intrinsic catalytic activity, the resulting F-NPC catalyst exhibits excellent bifunctional catalytic activities for both ORR and OER in alkaline mediums. Furthermore, the assembled Zn-air battery with F-NPC catalyst shows a high peak power density of 206.3 mW cm−2 and great stability, surpassing the commercial Pt/C + RuO 2 catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Core-shell MnCo 2 O 4 @NiFeRu-LDH on Ni foam was synthesized by hydrothermal method. • MnCo 2 O 4 @NiFeRu-LDH/NF can function as highly effective electrocatalyst toward OER. • The unique 3D nanoarchitecture and synergistic effects result in high performance. • An efficient acid/alkali water electrolyzer was set up using as-prepared anode. • The electrolyzer yields a current density of 100 mAcm−2 with voltage only 0.94 V. The development of high-efficiency oxygen evolution reaction (OER) electrocatalysts is of great importance for electrolytic H 2 generation. In this work, we report in-situ growth of MnCo 2 O 4 nanoneedles and NiFeRu layered double hydroxide (LDH) nanosheets on nickel foam (NF) (MnCo 2 O 4 @NiFeRu-LDH/NF) that can function a highly efficient electrode toward electrocatalysis of OER. Such electrode demands an overpotential of as low as 205 mV to reach 10 mA cm−2 in alkaline electrolyte and can run stably over 120-hours continuous operation. A hybrid flow acid/alkali electrolyzer is set up by using the Pt/C as the acidic cathode coupling with the MnCo 2 O 4 @NiFeRu-LDH/NF as the alkaline anode, which only requires an applied voltage of 0.59 V and 0.94 V to attain an electrolytic current density of 10 mA cm−2 and 100 mA cm−2, respectively. The present work could push forward the further development of the electricity-saving electrolytic technique for H 2 generation. [ABSTRACT FROM AUTHOR]

Transforming carbon dioxide (CO 2) into valuable fuels or chemicals through electrolysis represents a promising approach to reduce the carbon footprint. Conventional CO 2 electrolysis yet faces a challenge in low energy efficiency due to the energy-intensive oxygen evolution reaction (OER) occurring at the anode. In this study, we present an advanced CO 2 electrolysis system that pairs cathodic CO 2 reduction with anodic degradation of hydrazine oxidation reaction (HzOR), enabling efficient CO 2 electrolysis at an ultra-low voltage. To achieve this objective, two precious-metal-free electrocatalysts have been designed and fabricated. Specifically, a nickel single-atom catalyst anchored on porous carbon nanofibers has been developed for cathodic CO 2 -to-CO conversion, while a flower-like Ni 2 Fe 2 N catalyst grown in-situ on nickel foam has been developed for anodic HzOR. We demonstrate high efficiency of CO production (FE CO > 80%) at 100 mA cm−2 with an applied voltage of only 0.45 V by simultaneously degrading hydrazine in a flow cell. [Display omitted] • A promising green electrolyzer coupling CO 2 reduction reaction with hydrazine oxidation reaction (HzOR) was proposed. • The single atomic nickel anchored on porous carbon nanofiber (NiSACs-PCNF) was developed as highly active CO 2 RR catalyst. • The flower-like Ni 2 Fe 2 N in-situ grown on nickel foam (Ni 2 Fe 2 N/NF) was prepared as the effective HzOR catalyst. • The assembled electrolyzer achieved efficient CO production and hydrazine degradation at an ultralow voltage of 0.45 V. • The designed electrolyzer provided a new route for coupling energy-efficient CO 2 upgradation with waste degradation. [ABSTRACT FROM AUTHOR]

The exploration of highly effective, durable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is vital in developing an alkaline electrolyzer for H 2 generation. Although binary transition metal oxides, particularly spinel ferrites with a general chemical formula MFe 2 O 4, are a promising class of candidates for OER, their intrinsically low electrical conductivity has a significant negative impact on their electrochemical performances. Herein, we report a simple one-step method for tailoring carbon spheres (CSs) with CoFe 2 O 4 (CFO) to form a CFO@CSs composite as a cost-effective electrocatalyst. The as-synthesized CFO@CSs features a high specific surface area of 56.94 m2/g and exhibits decently high OER catalytic activity with a relatively small overpotential of 390 mV at 10 mA/cm2, fast kinetics, and high durability in alkaline medium. Moreover, the pairing of the bare Ni mesh electrode as the cathode and the CFO@CSs on Ni mesh as the anode is set up to illustrate its feasibility for the overall alkaline water splitting. This study offers a cost-effective electrocatalyst for OER that can be used instead of precious metals in various renewable energy storage and conversion applications. CoFe 2 O 4 @carbon spheres nanohybrid (CFO@CSs) electrocatalyst was successfully prepared with a facile one-step solvothermal method, which shows excellent electrocatalytic OER performance with low overpotentials of 390 mV at 10 mA cm−2 OER. The assembled system CFO@CSs/NM||bare NM also shows good catalytic performance and excellent stability of the overall water splitting in alkaline media. [Display omitted] [ABSTRACT FROM AUTHOR]

Exploring low-cost, highly efficient, and sustainable non-precious electrocatalysts for electrolytic H 2 generation is driving research for the sustainable green urban development. Herein, we present a simple synthetic approach, through a two-step process, to prepare the bifunctional electrode of Co 3 O 4 –C@FeMoP hybrid micro rods/nanosheets anchored on nickel foam (NF), in which the Co 3 O 4 –C microrods grown on NF surface are decorated by FeMoP nanosheet layers, which is directly grown through a simple hydrothermal followed by post-phosphorization processes. The obtained hybrid hierarchical Co 3 O 4 –C@FeMoP/NF shows a significant enhancement in the electrocatalytic activities of oxygen/hydrogen evolution reactions (OER/HER) in comparison to the individual Co 3 O 4 –C and FeMoP nanostructures, thanks to more heterointerface active sites provided by FeMoP nanostructures with three-dimensional (3-D) layered architectures. The Co 3 O 4 –C@FeMoP/NF catalyst exhibits a relatively small overpotential of 200 mV vs. RHE for OER to achieve 20 mA/cm2 and 123 mV vs RHE at 10 mA/cm2 for HER along with excellent durability in alkaline electrolytes. We demonstrate the bifunctional electrocatalytic electrode as the electrolyzer for the generation of H 2 via water splitting at small applied voltage of 1.61 V to achieve 10 mA/cm2 and good stability for 24-h continuous running. • Synthesis of high-activity catalyst material Co 3 O 4 –C@FeMoP/NF. • Decent electrocatalytic activity toward OER and HER in alkali. • Alkaline water electrolysis system with bifunctional electrocatalyst electrode. [ABSTRACT FROM AUTHOR]

• V 8 C 7 /CoP were prepared through pyrolysis and a subsequent phosphidation. • V 8 C 7 /CoP exhibits a splendid electrocatalytic activity toward HER, OER and UOR. • A V 8 C 7 /CoP-AAAE was set up for energy-saving electrolytic hydrogen production. Hydrogen production via water electrolysis for large scale application is still limited majorly by the huge energy consumption and high cost of catalyst materials. In this work, with rationally designing V/Co metal-organic framework (V/Co-MOF) as a precursor, a series of V 8 C 7 decorating CoP nanosheets-assembled microspheres (V 8 C 7 /CoP) was synthesized via pyrolysis and a subsequent phosphidation. Thanks to the synergistic effect between V 8 C 7 and CoP, the optimized V 8 C 7 /CoP as trifunctional catalysts exhibit remarkable performance toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and urea oxidation reaction (UOR). More importantly, we propose an acid-alkaline asymmetric-electrolyte electrolyzer (AAAE) by using the optimized V 8 C 7 /CoP electrode as both acidic cathode for HER and alkaline anode UOR, respectively. The optimum AAAE system only needs an applied voltage of 0.8 V to reach an electrolytic current density of 10 mA cm−2 for hydrogen production, which significantly reduces the energy consumption for hydrogen production owing to the assistance of electrochemical neutralization energy (ENE) and electrochemical urea oxidation energy. [ABSTRACT FROM AUTHOR]

Hydrogen, as the one of clean energy source, has the advantages of high energy density and carbon-free emission. Water electrolysis is one of the most promising ways to generate hydrogen, but the rather high energy required seriously hinders its widespread applications yet. In this study, we report an alkaline electrolyzer to implement energy-saving H 2 generation by coupling cathodic hydrogen evolution reaction (HER) with anodic glucose oxidation reaction (GOR) other than oxygen evolution reaction, in which nickel-doped MoS 2 nanoparticles (Ni–MoS 2 NPs) has been developed as bifunctional electrocatalyst for HER and GOR. The electrolyzer only requires a cell voltage of 1.67 V to reach an electrolysis current density of 10 mA cm−2, about 270 mV lower than the corresponding value in the traditional electrolyzer. Electrolytic H 2 generation with the assistance of biomass derived materials may open a new way for the future sustainable development. • Ni-doped MoS 2 was fabricated as bifunctional electrocatalyst. • Biomass derived glucose as the electron donor to replace water. • Glucose assisted electrolytic H 2 generation can reduce energy consumption. [ABSTRACT FROM AUTHOR]

• Bifunctional electrocatalyst of Pd decorating P, N-codoped carbon nanostructures. • A hybrid acid/alkali cell for energy-saving and self-powered generation of H 2. • Indirect releasing H 2 stored in hydrazine by an electrochemical strategy. • Efficient, controllable and continuous release high-purity H 2 from H 2 carrier. Liquid-phase hydrogen (H 2) carriers have received widespread attention owing to their convenient and safe storage and transportation of H 2. Among the various liquid-phase H 2 carriers, hydrazine (N 2 H 4) shows promising applications due to its ability to release H 2 in aqueous solutions via the dehydrogenation process with the assistance of suitable catalysts, which yet produces N 2 /H 2 mixture gas and thus require additional high-energy purification process. In this work, we propose a self-powered electrochemical strategy to indirectly release high-purity H 2 stored in N 2 H 4 by developing a hybrid acid/alkali electrochemical cell, which is set up by coupling alkaline anode for N 2 H 4 electrooxidation reaction (HzOR) with acidic cathode for hydrogen evolution reaction (HER), respectively. For this purpose, Pd nanoparticles uniformly decorating P, N-codoped hollow dodecahedron carbon nanostructures (Pd/PNC) is prepared as bifunctional electrocatalyst for both HzOR and HER, which exhibits high electrocatalytic activity and robust stability. Density functional theory (DFT) calculations imply that P, N-codoping substrate of Pd is conductive to optimize adsorption/desorption sites upon electrocatalysis of HzOR and HER by lowing Gibbs free energy and improving activity. The as-assembled hybrid acid/alkali cell is capable of delivering a maximum power density of 18.2 mW cm−2 and can run stably for 120 h, implementing H 2 generation in a voltage or power controllable manner. This work may inspire exploring the way for efficient, energy-saving, and continuous generation of high-purity H 2. [ABSTRACT FROM AUTHOR]

Exploring efficient and low-cost oxygen evolution reaction (OER) electrocatalysts is of crucial importance. Here, we report a surface plasmon resonance (SPR) engineering strategy to regulate surface reconstruction of CoFeB nanosheets by decorating plasmonic MoO 2 nanospheres (MoO 2 /CoFeB), in which the SPR effect of MoO 2 offers an additional acceleration for the conversion of inactive Co species to active cobalt oxyhydroxide on the CoFeB surface under visible light. Our results also indicate the real reactive surface for CoFeB is in the form of CoFeOOH with adsorbed BO 2 − that has positive effect. The MoO 2 /CoFeB shows superior OER performance with a low overpotential (209 mV at J =10 mA cm−2). However, such an accelerated reconstruction behavior would be self-terminated once the anodic voltage increases to thoroughly oxidize the MoO 2 to high valence state (+6). This work inspires us to develop a rational strategy to improve the catalytic performance by properly regulating the surface reconstruction. [Display omitted] • SPR effect of MoO 2 was applied for regulating surface reconstruction of CoFeB to enhance the electrocatalytic OER process. • The MoO 2 /CoFeB nanohybrid electrocatalyst shows attractive OER performance with a low overpotential of 209 mV at 10 mA cm–2. • An insightful fundamental understanding of the reaction interface for metal borides was presented. [ABSTRACT FROM AUTHOR]

Ammonia is a vital chemical raw material for both industry and agriculture, the current ammonia synthesis process is based on the Haber-Bosch process yet faces issues of high-energy consumption and high CO 2 emission. Electrochemical nitrite reduction reaction (NO 2 −RR) has been considered as one of the alternative paths for ammonia synthesis. Here, we develop a large-scale viable route for synthesis of 2H–MoS 2 nanosheets (MoS 2 NSs), which show high activity as electrocatalyst for high-efficiency conversion of NO 2 −RR to ammonia, the yields of NH 3 production rate reaches as high as 8.99 mg cm−2 h−1 with a faradaic efficiency of 93.52%. A hybrid electrolytic cell is constructed by coupling MoS 2 NSs as NO 2 −RR cathode in neutral electrolyte with oxygen evolution reaction (OER) in alkaline solution, which can operate stably for more than 120 h with the capability of continuously producing ammonia at the production rate of 38.79 mg cm−2 h−1. • Scalable molten-salt-assisted synthesis MoS 2 nanosheets (MoS 2 NSs). • MoS 2 NSs can effectively electrocatalysis nitrite to NH 3 in neutral media. • The Faradaic efficiency from nitrite to NH 3 catalyzed by MoS 2 NSs reaches 93.52%. • Neutral/alkaline electrolyzer was built for NH 3 production (stability: >120 h). [ABSTRACT FROM AUTHOR]

• A facile dual-sites method is developed to modify MoO 2 nanospheres. • The optimal Ni and Fe co-doped MoO 2 shows low overpotential and good stability. • The synergistic catalytic mechanism for OER is illustrated. Oxygen evolution reaction (OER) is of critical importance in the area of electrocatalysis as it is frequently involved in a diversity of electrochemical devices. Molybdenum-based materials, thanks to their metallic character induced high conductivity, have been widely studied as catalysts for a variety of reactions but few reports for oxygen evolution reaction (OER). Herein, we report a dual-sites modifying strategy to modulate electrocatalytic properties of metallic MoO 2 nanospheres toward OER, which is implemented by a one-pot synthesis process to prepare nickel and iron co-doped molybdenum oxide (Mo 0.9 Ni 0.05 Fe 0.05 O 2). The introduction of dual sites (i.e. , Ni and Fe) on MoO 2 nanospheres surface can tune the surface electronic structure and local-chemical environment with generation of high-valence Mo and hydroxyl-rich surface, synergistically contributing to the improved electrocatalytic performance in terms of stability and activity. Density functional theory (DFT) calculation indicates Fe-doping site favors for enhancing the turnover efficiency (TOF) while the Ni-doping site facilitates the first proton coupled electron transfer (PCET) upon electrocatalysis of OER. The Mo 0.9 Ni 0.05 Fe 0.05 O 2 requires only 249 mV of overpotential to reach a current density of 10 mA cm−2 with excellent stability for 80 h. This study expands the research on molybdenum-based OER catalysts and gains insight into the origin of both the activity and stability of Ni/Fe-doping reactive sites. [ABSTRACT FROM AUTHOR]

• RuCo@NG/N-GNs catalyst were fabricated via one-step annealing strategy. • RuCo@NG/N-GNs holds unique structure and plenty of active sites. • RuCo@NG/N-GNs exhibits a top-level acidic OER and alkaline HER performance. • DFT calculations reveals the critical role of Co in enhancing HER and OER. There remain certain critical issues for hydrogen production in both proton exchange membrane (PEM) and alkaline water electrolysis, the former of which faces daunting challenges in the development of high-activity and high-stability catalysts for acidic oxygen evolution reaction (OER), while the latter one strongly demands enhancing the sluggish kinetic of alkaline cathodic hydrogen evolution reaction (HER). Herein, we reported a facile one-step annealing strategy for fabricating hybrid electrocatalyst with RuCo alloy nanoparticles encapsulated by N-doped graphite loading on N-doped graphite nanosheets (RuCo@NG/N-GNs), which manifests highly desirable electrocatalytic features toward both acidic OER and alkaline HER with impressively high activity, fast kinetic and excellent stability. The optimized RuCo@NG/N-GNs requires a quite low overpotential of 209 mV at 10 mA cm−2 for acidic OER with a quite low Tafel slope of 56 mV dec−1, and demands a striking low overpotentials of 9 mV at 10 mA cm−2 toward alkaline HER with a Tafel slope of as low as 30 mV dec−1. Experiments combined with density functional theory (DFT) calculations reveal that the critical role of Co element in enhancing the HER and OER performance. For HER, the surface Co improves the oxophilicity of catalyst that indirectly aids the proton donation in alkaline; and for OER, surface Co itself acts as active sites to directly aid the reaction. The relatively low-cost electrocatalyst in this work is expected to inspire more innovative researches to step forward the large-scale commercial practice feasibility of PEM and alkaline water splitting. [ABSTRACT FROM AUTHOR]

A bifunctional electrode with 1D nickel–iron phosphide and molybdenum dioxide (NFPMO) grown on nickel foam presents highly outstanding electrocatalytic performance for overall water splitting. • Electrode of NiFeP-MoO 2 hybrid nanorods on Ni foam for water electrolysis. • High-activity and high-stability electrocatalyst towards HER and OER. • The voltage for water splitting at j = 10, 100 mA cm−2 is only 1.41 V and 1.65 V. The research about inexpensive and efficient electrocatalyst plays a significant role in electrocatalyzing H 2 production from water splitting. We herein report a novel hybrid 1D heterogeneous nanorods based on nickel–iron phosphide and molybdenum dioxide (NFPMO) grown on nickel foam that presents highly outstanding electrocatalytic performance in electrochemical overall water splitting, both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The applied cell voltage of employing NFPMO electrode in overall water splitting merely require 1.41 V and 1.65 V at 10 mA cm−2 and 100 mA cm−2 working electrolysis current density, respectively, and it can bear high stably upon hundreds of hours long-term electrolysis operation. The synergistic effects of heterogeneous structure in 1D nanorods obviously accelerate the electrocatalytic activity, as demonstrated by not only electrochemical tests but also coupling systematic electrochemical study with density functional theory (DFT) calculation. [ABSTRACT FROM AUTHOR]

A bifunctional electrocatalyst has been developed through integrating nickel–iron (oxy)hydroxide nanoparticles (NiFeO x (OH) y) and MoS 2 nanosheets on reduced graphene oxide. It has been deduced that MoS 2 is oxidized during oxygen evolution reaction, and the oxidized Mo species modulate the electronic structure of NiFeO x (OH) y , while NiFeO x (OH) y serves as water dissociation promoters to facilitate hydrogen evolution reaction, resulting in high electrochemical activity and durability for overall water splitting in alkaline electrolyte. • The composites consisting of NiFeO x (OH) y and vertically-oriented MoS 2 nanosheets on reduced graphene oxide has been prepared. • The promoting roles of MoS 2 nanosheets on oxygen evolution reaction have been proposed. • The integrated electrocatalyst shows high activity and superior durability for water splitting. Developing cost-effective methodologies for fabricating efficient bifunctional electrocatalysts is pivotal to boost electrochemical water splitting. Herein, we report an integrated composite, which is composed of NiFeO x (OH) y nanoparticles and vertically-oriented MoS 2 nanosheets on reduced graphene oxide (rGO) matrix (NiFeO x (OH) y @MoS 2 /rGO), for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). It has been deduced that MoS 2 is oxidized during OER, and the oxidized Mo species modulate the electronic structure of NiFeO x (OH) y to facilitate chemisorption of the oxygen species in OER. Meanwhile, NiFeO x (OH) y speeds up sluggish water dissociation in HER, and thus significantly improving HER activity of MoS 2 in alkaline electrolyte. The integrated composite shows high electrocatalytic activity and superior durability for HER and OER with low overpotentials of 170 mV at 10 mA cm−2 and 250 mV at 20 mA cm−2, respectively. This work provides new approaches to develop electrocatalysts for overall water splitting and other applications. [ABSTRACT FROM AUTHOR]