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Summary: The development of highly active, robust and cost‐effective noble metal‐free electrocatalysts for hydrogen evolution reaction (HER) in alkaline solution remains a severe challenge. In this work, a hollow structure CoSe2‐FeSe2 heterojunction electrocatalyst (denoted by "(Co,Fe)Se2") was designed by a simple anion exchange reaction and selenization. Benefiting from the unique hollow structure, the (Co,Fe)Se2 catalyst accelerates diffusion of electrolyte, besides, the CoSe2‐FeSe2 heterojunction could provide rapid interfacial charge transportation and more active sites for the HER reaction. The (Co,Fe)Se2 electrode material exhibits good performance for HER in 1 M KOH electrolyte. It needs an overpotential of 124 mV to obtain a current density of 10 mA cm−2, and the Tafel slope is 65 mV dec−1. Besides, (Co,Fe)Se2 has a smaller charge transfer resistance compared with CoSe2. At the same time, it has relatively large electrochemical active surface area due to the porosity. Most importantly, the (Co,Fe)Se2 electrode displays good stability in alkaline conditions for 15 hours, the linear sweep voltammetry curves are almost coincident before and after 1000 cycles, the overpotential with current density of 10 mA cm−2 increased by only 9.76% after 5000 cycles of CV. It shows great application potential in HER. [ABSTRACT FROM AUTHOR]

Following the ammonia treatment, the pores created by the folds allow for electrolyte storage and facilitate ion transport. The interlayer spacing between MXene nanosheets widens due to the volume increase when water freezes. The generous ion transport paths and redox-active ammonium ions offer higher specific capacity and faster reaction kinetics. [Display omitted] Ti 3 C 2 T x MXene demonstrates excellent potential as an anode material for sodium-ion capacitors. However, the narrow interlayer spacing and self-stacking phenomenon limit its applicability. In this study, we demonstrate an easy two-step method involving freezing and crumpling of MXene nanosheets to improve their Na-ion storage via the addition of ammonium ions (referred to as FCM nanosheets). Flat MXene particles aggregate and undergo folding in an alkaline solution. Ammonium ions can penetrate the gaps between MXene nanosheets, expanding interlayer spaces and inducing the formation of folds. Compared to MXene nanosheets, FCM nanosheets exhibit improved ion transfer kinetics and additional high capacity owing to the intercalated ammonium ions. The manufactured FCM anode exhibits remarkable electrochemical properties, including a high specific capacity of 313 mAh g−1 and stability over 15,000 cycles. [ABSTRACT FROM AUTHOR]

Seeking the efficient and robust electrocatalysts necessarily enhances performance of hydrogen evolution reaction (HER). Increasing the surface active sites is a means to improve the performance. Herein, we use the Ni 0·85 Se anchored on reduction of graphene oxide (Ni 0·85 Se/rGO) hybrid material skillfully established by one-step facile hydrothermal method as a robust and stable electrocatalyst applying to hydrogen evolution reaction (HER). In terms of morphology, Ni 0·85 Se nanospheres composed of many nanosheets are uniformly distributed on the graphene sheet layer. We also detailedly analyze its properties. Based on the interaction between Ni 0·85 Se and rGO, and the roles of graphene are as a substrate to heighten conductivity, possesses more active surface area by limiting growth of Ni 0·85 Se, and increases dispersion for exposing more active surface area and enlarge ion/electron transfer rate. In HER, the Ni 0·85 Se/rGO catalyst displays the overpotential of 128 mV with a common current density of 10 mA cm−2, a small Tafel slope of 91 mV dec−1, an extremely low onset potential of 37 mV, outstanding stability that a high current retention of 97.7% after 1000 cycles and well long-term stability for 18 h, outperforming the capability of Ni 0·85 Se nanospheres in alkaline solution for HER. The above results indicate that the Ni 0·85 Se/rGO hybrid material is a good HER ability and non-noble metal electrocatalyst has potential value in HER. • The Ni 0.85 Se nanospheres uniformly decorate the rGO sheets. • The Ni 0.85 Se/rGO electrocatalyst possesses more active surface area. • The stability of the composites can reach 97.7%. • The hybrid material exhibits superior performance for HER. [ABSTRACT FROM AUTHOR]

In this paper, we report the three-dimensional self-supported CoMoO 4 nanosheet clusters on the nickel foam (denoted as CoMoO 4 /NF) by a facile hydrothermal-calcination method for efficient hydrogen generation. As a result, the freestanding CoMoO 4 electrode exhibits an efficient electrochemical activity towards hydrogen evolution reaction, showing overpotentials as low as 68 and 178 mV at current densities of 10 and 100 mA cm−2 in the alkaline condition (1 M KOH), respectively, a Tafel slope value of 82 mV per decade. Moreover, the electrode exhibits remarkable electrochemical durability for 1000 cycles. Significantly, the water splitting electrolyzer assembled with CoMoO 4 /NF || NiFe LDH/NF (the nickel iron layered double hydroxide supported on the nickel foam) system achieved 20 mA cm−2 at 1.63 V, showing the CoMoO 4 /NF is promising for practical water splitting applications. • The low-cost and effective transition metal oxide of CoMoO 4 was adopted for hydrogen generation. • The open nanostructure can facilitate permeating electrolyte as well as releasing hydrogen molecules. • The crosslinked nanosheet clusters can offer amounts of active sites for hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Silver particles with microspheric structure are directly electrodeposited on carbon fiber cloth (CFC) substrate by square-wave potential electrodeposition method. The electrocatalytic behaviors of the Ag/CFC electrode toward hydrazine oxidation in alkaline solution are examined by cyclic voltammetry and chronoamperometry. An onset oxidation potential of -0.5 V and a peak current density of 30 mA cm −2 are achieved in the solution containing 1.0 mol L −1 KOH and 20.0 mmol L −1 hydrazine. The microspheric structure of the Ag/CFC electrode provides large electroactive surface area, hence, abundant active sites are vacant for hydrazine oxidation. The calculated apparent activation energies at different potentials show that hydrazine electro-oxidation at higher potential has faster kinetics than that at lower potential. In addition, the transfer electron number of hydrazine oxidation reaction on the Ag/CFC electrode is close to four, suggesting hydrazine is almost completely electrooxidized on the electrode and the full use of hydrazine fuel is basically achieved. [ABSTRACT FROM AUTHOR]

Fully metallic nickel nanowire arrays (NWAs) electrode is prepared by electrodepositing nickel within the pores and over-plating on the surface of polycarbonate template (PCT) with subsequent dissolution of the template in dichloromethane. The as-prepared electrode is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Urea electro-oxidation reaction in KOH solution on the nickel NWAs electrode is investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The results show that the nickel NWAs electrode achieves an onset oxidation potential of 0.25 V (vs. Ag/AgCl) and a peak current density of 160 mA cm −2 in 5 mol L −1 KOH and 0.33 mol L −1 urea accompanied with considerable stability. [ABSTRACT FROM AUTHOR]