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In order to alleviate the energy crisis and propel a low-carbon economy, hydrogen (H2) plays an important role as a renewable cleaning resource. To break the hydrogen evolution reaction (HER) bottleneck, we need high-efficiency electrocatalysts. Based on the synergistic effect between bimetallic oxides, hierarchical mesoporous CoNiO2 nanosheets can be fabricated. Combining physical representations with electrochemical measurements, the resultant CoNiO2 catalysts present the hierarchical microflowers morphology assembled by mesoporous nanosheets. The ultrathin two-dimensional nanosheets and porous surface characteristics provide the vast channels for electrolyte injection, thus endowing CoNiO2 the outstanding HER performance. The excellent performance with a fewer onset potential of 94 mV, a smaller overpotential at 10 mA cm−2, a lower Tafel slope of 109 mV dec−1 and better stability after 1000 cycles makes CoNiO2 better than that of metallic Co and metallic Ni. [ABSTRACT FROM AUTHOR]

The electrochemical nitrate reduction reaction (eNO 3 RR) to ammonia (NH 3) is a promising alternative method to the Haber-Bosch process that requires high temperature and pressure. In this contribution, the integrated Co 3 O 4 nanowire arrays on Ni foam (Co 3 O 4 /NF) are reported to exhibit the outstanding performance with a high NH 3 yield rate of 117.01 mg h−1cm−2, a superior NH 3 Faradaic efficiency of 99.28 %, a high effective current density of 1475.71 mA cm−2, and a good operation durability during 40 consecutive recycling tests (40 h) in 1.0 M NaOH (0.1 M NaNO 3). The high-valence metal cations as electron-deficient centers can act as Lewis-acid sites, favorably interacting with the Lewis base NO 3 −, and accordingly boosting the NO 3 − adsorption and activation. Moreover, the in-situ growth array configuration provides the substantial active sites and constructs a fast electron-transport channel, thus facilitating the conversion of NO 3 −-to-NH 3. Density functional theory (DFT) calculations also reveal that the Co atoms as the active sites are preferred to adsorb NO 3 −, implying that the NO 3 − electroreduction dominates the cathodic reaction rather than hydrogen evolution reaction. This study provides a viable method to design integrated electrodes with enhanced eNO 3 RR activity and selectivity, which might have broad prospects in the application of renewable energy. The efficient nitrate-to-ammonium conversion is achieved by the integrated Co 3 O 4 nanowire arrays rich in electron-deficient centers. Benefitted from the massive exposed active sites, improved conductivity and charge transfer efficiency, as well as the abundant Lewis acid sites, Co 3 O 4 nanowire arrays present the brilliant nitrate electroreduction performance, including 117.01 mg h−1 cm−2 NH 3 yield rate and 99.28 % Faradaic efficiency in 1.0 M NaOH with 0.1 M NO 3 −. [Display omitted] • High-valence metal cations are favorable to boost NO 3 − adsorption and activation. • Integrated nanowire arrays configuration can provide massive exposed active sites. • Co 3 O 4 /NF can provide a fast electron-transport channel and excellent conductivity. • Co 3 O 4 /NF presents the considerable activity and stability towards eNO 3 RR process. [ABSTRACT FROM AUTHOR]

The exploitation of efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is the key to the industrialization of the hydrogen production technology from water splitting. Herein, Ni 1 Fe 2 @Fe 2 O 3 composites with core-shell structure embedded in Metaplexis japonica fluff-derived carbon microtube matrix (Ni 1 Fe 2 @Fe 2 O 3 @C) are prepared by nitrate soaking and subsequent high-temperature calcination, which are used to catalyze the OER. The existence of carbon matrix greatly prevents the agglomeration of metal particles and creates an efficient electron transfer path for OER. The synergy among the carbon matrix, Ni 1 Fe 2 core and Fe 2 O 3 shell together enhances the OER performance, thus endowing Ni 1 Fe 2 @Fe 2 O 3 @C with the considerable catalytic activity with the overpotential of 271 mV at 10 mA cm−2 and a Tafel slope of 78 mV dec−1. Ni 1 Fe 2 @Fe 2 O 3 @C also shows good stability due to the double protection of metal particles by biomass carbon matrix and ultrathin Fe 2 O 3 shell. The water splitting device composed of Pt/C as the cathode and Ni 1 Fe 2 @Fe 2 O 3 @C as the anode exhibits water splitting activity close to that of Pt/C || RuO 2 system in alkaline medium, and the stability retention rate of the system reaches to 93 % after 30 h electrolysis. [Display omitted] • Ni 1 Fe 2 @Fe 2 O 3 composites with core-shell structure embedded in Metaplexis japonica fluff-derived carbon microtube matrix were prepared. • The existence of carbon matrix greatly prevents the agglomeration of metal particles and creates an efficient electron transfer path for OER. • Ni 1 Fe 2 @Fe 2 O 3 @C exhibits considerable catalytic activity with the low overpotential for OER. [ABSTRACT FROM AUTHOR]

The design of inexpensive bifunctional electrocatalysts with excellent catalytic activity is crucial for the cost reduction from water splitting. As a kind of biomass with hollow tubular structure, Metaplexis japonica fluff is expected to be a natural substrate for the growth of nanostructured electrocatalysts. Herein, nanowire-like NiCo precursors are grown on Metaplexis japonica fluff biomass substrates by hydrothermal method, which are then converted into carbon microtube supported NiCoP-NiS 2 composites (NiCoP-NiS 2 /CMT) by low-temperature phosphorization and sulfidation treatment. As expected, the biomass substrate provides a guiding role for the growth of NiCoP-NiS 2 nanowires, which is conducive to expose more active areas and promote charge transfer during the reaction. As a result, the obtained NiCoP-NiS 2 /CMT exhibits good electrocatalytic performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, which only requires overpotentials of 134 and 308 mV at 10 mA cm−2, respectively. In addition, the constructed symmetric water splitting device exhibits a cell voltage of 1.62 V at 10 mA cm−2, and it also displays good stability during the 24 h test. [Display omitted] [ABSTRACT FROM AUTHOR]

Designing earth-abundant hydrogen evolution reaction (HER) electrocatalysts with superior performance and eminent stability is the key to the practical production of high purity hydrogen. In the present work, Mn oxides with various valence state complex Fe–Ni sulfide (Mn x O y @FNS) heterogeneous materials were successfully fabricated through a feasible two-step hydrothermal process and can be directly used as active and efficient HER electrodes in alkaline media. This binder-free and defect-rich catalyst barely requires 105 and 365 mV to achieve −10 and −500 mA cm−2, respectively. Profiting from the disordered structure and the efficient interfacial effects between Mn oxides and Fe–Ni sulfide (FNS), this heterogeneous catalyst reveals sufficient electroactive sites, ample active edges and optimal electroconductivity. Additionally, during the 20 h HER reaction, the Mn x O y @FNS electrode exhibits outstanding durability. • Interlaced and plicated nanostructure provides sufficient exposed edge. • The disordered structure in Mn x O y @FNS afford plentiful electroactive sites. • This binder-free and defect-rich Mn x O y @FNS needs 105 to attain −10 mA cm−2. • This electrocatalyst exhibits excellent HER stability. [ABSTRACT FROM AUTHOR]