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• 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]

[Display omitted] • A hypotoxic molten-salt-assisted method was developed to synthesize Co 2 P (t-Co 2 P). • The t-Co 2 P can spontaneously transform into CoOOH in alkaline solutions. • The t-Co 2 P can effectively electrocatalysis acidic hydrogen evolution reaction. • CoOOH can effectively electrocatalysis alkaline sulfite (SO 3 2–) oxidation. • A hybrid acid-alkali electrolyzer was built for H 2 generation and sulfite removal. Co 2 P has been widely applied in a variety of applications yet still faces challenges in implementing hypotoxic and large-scale synthesis. We here report a scalable synthetic route to produce tussock-like nanostructured Co 2 P (t-Nano Co 2 P), which exhibits high-performance electrocatalytic properties toward acidic hydrogen evolution reaction (HER). Such t-Nano Co 2 P can evolve to CoOOH nanoplates that show excellent electrocatalytic activity for sulfite oxidation reaction (SOR) in alkaline solution. The findings encourage us to construct a hybrid acid/alkali electrolyzer with t-Nano Co 2 P and its CoOOH derivative as catalysts of acidic cathode for HER and alkaline anode for SOR, respectively, which performs excellently with capability of synchronous generation of H 2 and sulfate in an industrial-level rate at a relatively low applied voltage. The proof-of-concept electrolyzer, by virtue of the viability of scalable synthesis and high-production yield, holds great promise for co-production of H 2 and sulfate in an energy-effective and environmentally-friendly manner. [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]