α-SnSe is one of the most promising thermoelectric materials with low thermal conductivity and a high power factor. Since the thermoelectric properties of a material have a strong dependence on its crystal structure, we study the energetic and thermoelectric properties of four new monolayer phases of SnSe (β, γ, δ and ε) together with α-SnSe using the ab initio density functional theory method. The calculated electronic structures show that all five phases are semiconductors with different band gaps. The α, β, γ, and δ phases have an indirect band gap with the hybridization of sp orbitals, whereas the ε phase has a direct band with the hybridization of sp orbitals. The thermoelectric transport properties and coefficients are obtained from the electronic structure using semi-classical Boltzmann theory, and the results indicate that the four new phases of SnSe (β, γ, δ and ε) all have better thermoelectric properties compared with the reported α phase. The predicted ZT value for the β-SnSe phase is 2.06 at 300 K, suggesting that it has great potential for novel thermoelectric applications.

Development of noble-metal-free and active electrocatalysts is crucial for the oxygen evolution reaction (OER) in the water-splitting process. Herein, crystal Co x B catalysts (x = 1–3) of the OER are fabricated by a ball-milling method. Among these Co x B catalysts, Co2B exhibits the best OER activity, with a current density of 10 mA cm–2 at an overpotential of 287 mV in 1 M KOH solution. Such OER activity of Co2B is favorably comparable to that of the commercial IrO2 and most recently reported OER catalysts. Furthermore, the Co2B catalyst exhibits excellent stability with a stable current density of 50 mA cm–2 over 12 h of continuous electrolysis operation. X-ray photoelectron spectroscopy and cyclic voltammetry demonstrate that the B in Co x B makes oxidation easier, leading to their enhanced OER activities in comparison to metal Co. In addition, the Co2B electrocatalyst also exhibits high activity in the hydrogen evolution reaction; thus, the catalyst can be used as a bifunctional catalyst for full water splitting.

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B doping and surface engineering of a N-containing Co3C alloy at room temperature are simultaneously achieved, endowing the resultant catalyst with excellent and stable multifunctional activities.

Ultrasmall FeNi3N particles with an exposed active (110) surface anchored on nitrogen-doped graphene as multifunctional electrocatalysts for both overall water splitting and Zn–air batteries exhibited excellent electrochemical performance.

A noble-metal-free and highly efficient bifunctional catalyst for overall water splitting is greatly desirable to generate clean and sustainable energy carriers such as hydrogen, but enormous challenges remain. Herein, porous interconnected iron-nickel nitride nanosheets are designed and grown on carbon fiber cloth (FeNi-N/CFC); combining a facile electrodeposition method and in situ nitriding process. The as-synthesized FeNi-N/CFC, with a low mass loading of 0.25 mg cm , exhibits excellent catalytic activities for both the oxygen evolution reaction (OER) with 20 mA cm at an overpotential (η) of 232 mV and also the hydrogen evolution reaction (HER) with 10 mA cm at η=106 mV. As a bifunctional electrocatalyst for overall water splitting FeNi-N/CFC only requires a cell voltage of 1.55 V to drive a current density (j) of 10 mA cm and shows robust long-term durability at j>360 mA cm with a negligible change in current density over 60 h; revealing its promising application in commercial electrolyzers.

Larger-scale usage of the clean energies requires advanced energy storage and conversion techniques. Overall water splitting and zinc air systems are promising energy conversion and storage means, but need high-performance, lowcost, and highly stable bifunctional electrocatalysts to hydrogen evolution/oxygen evolution reactions (HER/OER) and OER/oxygen reduction reactions (ORR), respectively. Herein we develop a facile method to fabricate CoMn double hydroxide (DH) hollow spheres as high-performance trifunctional electrocatalysts for overall water splitting and zinc-air battery. The outmost surfaces of the CoMn DH hollow spheres are composed of ultrathin nanosheets with a thickness of approximately 2.5 nm. Owing to the hollow and ultrathin features, CoMn DH hollow spheres exhibit excellent activities and robust stabilities toward HER, OER, and ORR. The overall water electrolyzer assembled with the CoMn DH hollow spheres can drive a current density of 10 mA cm −2 at an overpotential of merely 420 mV in 1.0 M KOH, among the best reported metal oxides and hydroxides. Remarkably, each all-solid-state Zn air battery with the optimized CoMn DH hollow spheres air-cathode exhibited good cycling stability. Furthermore, two all-solid-state Zn air batteries in series can power 55 red LED and the two-electrode electrolyzer catalyzed by the optimized CoMn DH hollow spheres with excellent operation stabilities.

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