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Rational construction of low-cost and high-performance electrocatalysts for water splitting is crucial for the advancement of renewable hydrogen fuel. Hybridizing heterojunctions or noble metals is one typical strategy used to boost the electrocatalytic performance for either the oxygen evolution reaction (OER) or hydrogen evolution reaction (HER). Here, low-content CeOx (3.74 wt%) is introduced into Ni3Fe nanoparticle-encapsulated carbon nanotubes (Ni3Fe@CNTs/CeOx), with both the OER and HER activities boosted, as a bifunctional electrocatalyst for overall water splitting. The composite is derived by pyrolyzing a mixture of melamine/ternary NiFeCe-layered double hydroxide. The composite electrocatalyst requires low overpotentials of 195 and 125 mV at 10 mA cm−2 in 1.0 M KOH, respectively, which are superior to those of Ni3Fe@CNTs/NF (313 and 139 mV) and CeOx/NF (345 and 129 mV), and in particular, OER overpotentials of 320 and 370 mV at 50 and 100 mA cm−2, respectively. Moreover, the composite-assembled electrolyzer for overall water splitting requires a current density of 10 mA cm−2 at a decent cell voltage of 1.641 V. Furthermore, the enhancement is elucidated by the synergistic effect: the dual role of CeOx in boosting the OER and HER, the highly conductive carbonaceous CNTs, large electrochemically active surface area and low charge-transfer resistance. The results can offer an effective route for designing and preparing low-cost and high-efficiency electrocatalysts for electrocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Non-noble electrocatalysts (such as transition metal sulfides) have been attractive to substitute noble-metal catalysts for oxygen evolution reaction (OER) to advance the practical application of clean energy. Herein, a Fe-doped CoS2 nanoparticles supported CoS2 microspheres@N-doped carbon (Fe-CoS2/CoS2@NC) is prepared as an efficient OER electrocatalyst. The Fe-CoS2/CoS2@NC composite is derived by sulfurizing the metanilic-intercalated Co(OH)2 microspheres decorated with binary active CoFe-Prussian blue analogue (CoFe-PBA) nanoparticles. The obtained composite combines the advantageous characteristics for enhancing electrocatalytic performances: binary active Fe-CoS2 derived from CoFe-PBA, active CoS2, N-doped carbon scaffold to improve electronic conductivity, the appropriate specific surface area and meso/macroporous size distribution to afford rich active sites. The Fe-CoS2/CoS2@NC requires an overpotential of 300 mV to reach a current density of 10 mA cm−2 with a Tafel slope of 72 mV dec−1 in 1.0 M KOH, outperforming those of NC/CoS2, NC/Fe-CoS2 and CoS2. Furthermore, the enhancement is experimentally supported by the low charge-transfer resistance and the large electrochemical active surface area during the OER. The synthesis approach could be extended to provide a tunable hydroxide/PBAs precursor-based approach for designing and preparing hierarchical structures as electrocatalysts. [ABSTRACT FROM AUTHOR]

Designing efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) is of great importance to advance water splitting technology towards practical applications. Herein, we report the preparation of IrCo nanoparticles supported on nitrogen-doped carbon (IrCo/NC) as a HER electrocatalyst in acidic and alkaline electrolytes. The IrCo/NC composite is obtained by pyrolyzing an Ir-doped Co(OH)2 precursor on g-C3N4, and is endowed with N-doped carbon and uniform IrCo alloy nanoparticles via a crystal confinement resulting from the Ir-doping into the Co(OH)2 layer. Electrocatalytic analysis shows that the IrCo/NC electrode requires low overpotentials of 32 mV at 10 mA cm−2 in 0.5 M H2SO4 and 33 mV in 1 M KOH, which are superior to those of the Co/NC and IrCo alloys that are free of Ir-doping or N-doped carbon. The results provide a strategy for designing and preparing active noble–transition bimetallic alloy electrocatalysts as efficient HER catalysts. [ABSTRACT FROM AUTHOR]

Combining ultrasmall NiS2 nanodots with three-dimensional carnation-like CoS2 microstructures is demonstrated to be able to enhance the electrocatalytic activities for both the oxygen and hydrogen evolution reactions, leading to efficient overall alkaline water splitting. [ABSTRACT FROM AUTHOR]

The development of highly efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is of great importance in advancing the practical applications of green and sustainable hydrogen energy. Doping with either cations or non-metallic anions is a typical strategy used to improve the electrocatalytic activity for OER catalysts. In this study, an anion doped bimetallic selenide Co 0.75 Fe 0.25 (S 0.2 Se 0.8) 2 solid solution is prepared via the simultaneous sulfuration and selenylation of a scalably produced CoFe-layered double hydroxide (CoFe-LDH) precursor, using commercially available sulfur and selenium powders as S and Se sources, respectively. Electrocatalytic test shows that the anion doped bimetallic selenide Co 0.75 Fe 0.25 (S 0.2 Se 0.8) 2 electrode requires an overpotential of 293 mV and a low Tafel slope of 77 mV dec−1 at a current density of 10 mA cm−2 in an alkaline media, and it exhibits the significantly enhanced electrocatalytic performance for the OER compared with its counterparts of Co 0.75 Fe 0.25 S 2 and Co 0.75 Fe 0.25 Se 2. The enhanced electrocatalytic performance is supported experimentally by the results of charge-transfer resistance and electrochemically active surface area. Our LDH precursor-based protocol can provide a strategy to prepare non-metallic anion doped bimetallic selenides as efficient electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ir nanodots-decorated Ni 3 Fe nanoparticles/rGO are prepared as electrocatalysts. • Decent performances for OER, HER, and overall water splitting are achieved. • XPS result reveals the interfacial interaction between Ir and Ni 3 Fe species. • DFT calculations support the observed enhancement. Developing low-cost and high-performance electrocatalysts for water splitting is crucial for advancing the hydrogen production. However, the large-scale practical application is highly dependent on the use of precious catalysts (such as IrO 2 and Pt/C). Herein, a composite of Ir nanodots (7.7 wt%) decorated Ni 3 Fe alloy on reduced graphene oxide (Ir/Ni 3 Fe/rGO) is prepared via an impregnation-reduction method as a bifunctional electrocatalyst for overall water splitting. The low-content decoration enables the composite to exhibit attractive electrocatlytic performances: requiring overpotentials of 254 and 36 mV at a current density of 10 mA cm−2 for the oxygen and hydrogen evolution reactions (OER and HER) in 1.0 M KOH solution, respectively, which surpass those of Ni 3 Fe/rGO (280 and 264 mV) and Ir/rGO (340 and 150 mV). In addition, the electrocatalyst-assembled Ir/Ni 3 Fe/rGO||Ir/Ni 3 Fe/rGO electrolyzer affords a decent cell voltage of 1.570 V at a current density of 10 mA cm−2 for overall water splitting, which outperforms those of Ni 3 Fe/rGO||Ni 3 Fe/rGO (1.730 V), Ir/rGO||Ir/rGO (1.790 V), and commercial IrO 2 ||Pt/C (1.574 V). Furthermore, X-ray photoelectron spectroscopy (XPS) result reveals the strong interfacial interaction between Ir and Ni 3 Fe species, density functional theory (DFT) calculations reveal that Ir species favor water dissociation and optimize the H* adsorption energy for HER, and reduce OOH* energy for OER; all of which give rise to the observed enhancement. The results can provide an effective strategy for designing and preparing low-cost and promising electrocatalysts for water splitting. [ABSTRACT FROM AUTHOR]