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[Display omitted] Amorphous engineering and atomistic doping provide an effective way to improve the catalytic activity in the oxygen evolution reaction (OER) of transition metal layered double hydroxides. Herein, Cerium (Ce) was introduced into NiFe-based oxyhydroxide using a modified aqueous sol–gel procedure. Ce as an electron acceptor promoted the coupling oxidation of Ni2+/3+ in NiFe oxyhydroxide, and the activated oxyhydroxide showed excellent catalytic activity in OER. The amorphous NiFeCe oxyhydroxide electrocatalyst demonstrated great modified OER catalytic activity under alkaline conditions and excellent cyclic stability, with an overpotential of only 284 mV at 50 mA cm−2, which was significantly better than amorphous NiFe oxyhydroxide and crystalline NiFeCe oxyhydroxide. Theoretical investigations further indicated that the overpotential of the rate-determining step (*OOH deprotonation) decreased from 0.66 to 0.41 V after Ce doping and strong electron interaction, effectively reducing the dependence of proton activity in the solution of OER, and optimizing the adsorption/desorption process of related oxygen-containing species in the reaction. This work also provides a good reference for optimizing OER activity by using rare-earth-metal induced electronic regulation strategies. [ABSTRACT FROM AUTHOR]

[Display omitted] Oxygen reduction reaction (ORR) is an essential half-reaction in next-generation energy storage and conversion systems, such as metal-air batteries and fuel cells. However, its practical application is restricted by the slow intrinsic kinetics, and the high price and low storage of noble metal electrocatalysts. Herein, unique CoFe nanoparticles encapsulated in N -doped carbon (CoFe-NC-Z8-900) with high content graphite-N derived from CoFe-g-C 3 N 4 @ZIF-8 via stepwise pyrolysis is reported as effective ORR catalysts. The increase of graphitic nitrogen content can enhance both the electrical conductivity and the adsorption of oxygen-containing intermediates, resulting in improved catalytic performance. Fortunately, CoFe-NC-Z8-900 exhibits an exceptionally high half-wave potential (E 1/2) of 0.914 V in a 0.1 M KOH solution. The excellent ORR electrocatalytic activity can be mainly attributed to the synergistic effect of the CoFe bimetal and the relatively high content of graphite-N. This study offers a unique method for creating powerful nitrogen-doped carbon coated metal nanoparticle electrocatalysts. [ABSTRACT FROM AUTHOR]

Hierarchical Fe-doped NiV HMS with excellent catalytic performance toward OER has been successfully prepared by a facile cation-exchange method. Electrochemical results and density functional theory + U simulation manifest that Fe doping could regulate the electronic structure of NiV HMS, thus enhancing its catalytic activity. [Display omitted] Exploring highly active and inexpensive electrocatalysts for oxygen evolution reaction (OER) is considered to be one of the preconditions for the development of energy and environment-related technologies. Nickel-based layered double hydroxides (LDHs) are extensively-studied OER electrocatalysts, but they still require relatively high overpotentials to achieve threshold current densities. In this work, iron-doped nickel-vanadium hydroxide microspheres (Fe-doped NiV HMS) were synthesized by doping iron ions into the NiV HMS through a facile cation-exchange method. The Fe-doped NiV HMS are hollow hierarchical structure stacked by high-density perpendicularly-lying nanosheets, which provide enough space for electrolyte penetration and diffusion. Owing to optimized composition and hollow hierarchical structure, the Fe-doped NiV HMS exhibits excellent electrocatalytic performance, which possessed a very low running overpotential (255 mV at 10 mA cm−2) and a smallest Tafel slope (56 mV dec−1) compared with hierarchical NiV HMS toward OER. Electrochemical results and density functional theory (DFT) manifest that Fe doping could regulate the electronic structure of NiV HMS, thus improving its electrical conductivity and electron transfer rate, and thus enhancing its catalytic activity. This research provides a convenient way to prepare Ni-based hydroxides as promising OER catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] Exploring highly-efficient noble-metal-free electrocatalysts for oxygen reduction reaction (ORR) is crucial for preparation of rechargeable metal-air batteries. Herein, FeNi-mIm (guest) was loaded on the surface of ZIF-8 (host) via a novel host-guest strategy, and the resulting ZIF-8@FeNi(mIm) X precursors can be converted to FeNi SAs/N C catalysts with controllable structures. Robust metal-organic framework (MOF)-derived atomically dispersed Fe/Ni dual single atom electrocatalysts for ORR were developed, followed by pyrolysis of the precursors. Characterizations showed that the atomically-dispersed Fe/Ni active sites were uniformly embedded in the N -doped carbon framework. As a result, the ORR performance was obviously improved with lower half-wave potential (E 1/2 = 0.91 V) in alkaline media. Such improvement is mainly attributed to the synergy of fully-exposed bimetallic single atom active sites caused by the interaction of Fe/Ni 3d orbitals. The lower adsorption energy of intermediate hydroxyl groups on the active sites and the smaller ORR energy barrier were calculated by the density functional theory. The novelty FeNi SAs/N C catalysts showed faster ORR dynamics in the rate-determining step of four-electron transfer. The synthesis strategy reported here provides an efficient approach to construct high performance dual single-atom catalysts with fully-exposed active sites on the surface. [ABSTRACT FROM AUTHOR]

We successfully synthesized N -doped carbon frameworks embedded with ZnCo nanoparticles on the surface of Ag NWs (Ag@ZnCo/NCF nanohybrids) by pyrolyzing AgNW@ZIF-8@ZIF-67 precursors. The synergistic effect among the components of Ag@ZnCo/NCF contributed to the enhancement of electrocatalytic performance on overall water splitting. Metal-organic frameworks (MOFs)-derived catalysts exhibit highly-efficient hydrogen or oxygen evolution performance on water splitting. However, it is an urgent problem to construct bifunctional electrocatalysts for both hydrogen and oxygen evolution performance. Herein, we adopted Ag nanowires as templates to prepare one-dimensional Ag nanowire@ZIF-8@ZIF-67 precursors (1D AgNW@ZIF-8@ZIF-67). Through pyrolysis, AgNW@ZIF-8@ZIF-67 precursors transformed into nitrogen-doped carbon frameworks (NCF) embedded with zinc-cobalt (ZnCo) nanoparticles on the surface of Ag NWs (denoted as Ag@ZnCo/NCF nanohybrids). The nanohybrids were consisted of Ag NWs with good conductivity and ZnCo/NCF nanohybrids with rich accessible active sites. Benefiting from their large specific surface area, accessible active sites and synergistic effect among components, Ag@ZnCo/NCF nanohybrids exhibit lower overpotentials of 139 mV and 279 mV at the current density of 10 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution, severally. Compared with other catalysts, Ag@ZnCo/NCF nanohybrids possess smaller Tafel slope, indicating their higher catalytic activity. This work provides a new perspective for designing low-cost and highly efficient bifunctional electrocatalysts for overall water splitting. [ABSTRACT FROM AUTHOR]