Heterostructures Composed of N‐Doped Carbon Nanotubes Encapsulating Cobalt and β‐Mo₂C Nanoparticles as Bifunctional Electrodes for Water Splitting

Abstract

Herein, we demonstrate the use of heterostructures comprised of Co/b-Mo 2 C@N-CNT hybrids for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline electrolyte.T he Co can not only create awell-defined heterointerface with b-Mo 2 Cbut also overcomes the poor OER activity of b-Mo 2 C, thus leading to enhanced electrocatalytic activity for HER and OER. DFT calculations further proved that cooperation between the N-CNTs,Co, and b-Mo 2 Cr esults in lower energy barriers of intermediates and thus greatly enhances the HER and OER performance.T his study not only provides asimple strategy for the construction of heterostructures with nonprecious metals,but also provides indepth insight into the HER and OER mechanism in alkaline solution.Electrochemical conversion of H 2 Oi nto hydrogen fuel (2 H 2 O!2H 2 + O 2 )h as attracted great attention from the scientific community because of its potential to replace fossil fuels. [1] Thee lectrolysis of water involves two half reactions: the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER), for which highly efficient electrocatalysts,s uch as Pt for the HER and IrO 2 for the OER, are usually required. [2,3] However,t he low abundance and high cost of noble-metal catalysts significantly hinder their large-scale commercialization. [4] Therefore,i ti si mperative to develop highly efficient nonprecious bifunctional electrocatalysts for both the HER and OER using the same electrolyte. [5,6] Recently,m any earth-abundant, noble-metal-free catalysts for the half-cell reactions have been explored as potential substitutes.S pecifically,t ransition-metal-based carbides, [7] sulfides, [8] phosphides, [9] and selenides [10] exhibit optimum catalytic performance for the HER, and it has been established that molybdenum carbide (Mo 2 C) has excellent HER activity in both acidic and basic electrolytes because the d-band electronic structure of Mo is similar to that of the noble metal Pt. [11][12][13] Notably,t he combination of Mo 2 Cw ith transition metals can effectively reduce the amount of unoccupied dorbitals of Mo to further enhance the HER activity,o wing to the electron-rich nature of transition metals.A lthough Mo 2 C-based materials with superior HER properties have been widely reported, their low OER activity has become am ajor obstacle for overall water splitting.T od ate,t he investigation of Mo 2 C-based electrocatalysts for OER has been limited. In this context, Yu and co-workers synthesized Ni/Mo 2 Cn anorods coated with apolydopamine hybrid, which required an overpotential (h 10 ) of over 368 mV to reach ac urrent density of 10 mA cm À2 , [14] and Luo and co-workers reported aMo 2 C/carbon hybrid that required an h 10 value over 500 mV. [15] Thea bove results suggest that the development of an efficient Mo 2 C-based electrocatalyst to create aw ater electrolyzer is still ac onsiderable challenge. [16] Cobalt-based hybrids can greatly improve the OER catalytic activity of materials,i ncluding Co-N, [17] Co-...

Unconventional dual-vacancies in nickel diselenide-graphene nanocomposite for high-efficiency oxygen evolution catalysis

“…5(b), the V-NiSe model exhibits a lower Gibbs free energy (1.97 eV) of the RDS than that of V-SeNiSe model (2.41 eV), demonstrating a more favorable OER kinetics enabled by the unconventional dual V-NiSe. Accordingly, the overpotentials of V-NiSe and V-SeNiSe models are 0.74 and 1.18 V, respectively, comparable to those reported previously [51,52]. Computational results here thus suggest that the unusual V-NiSe structure provides an optimal and moderate reaction pathway for OER, ensuring the low onset potential and high catalytic activity, consistent with our experimental results.…”

Designing Atomic Active Centers for Hydrogen Evolution Electrocatalysts

“…Mo-based materials can not only be used as substrates,but also as active species for the HER. [183][184][185] However,t he rational design of efficient Mo-based catalysts and athorough understanding of the nature of the catalytic activity at the atomic scale still face enormous challenges.A st he first illustration, we [186] designed single Mo atoms supported on Ndoped carbon (Mo-SAC, Mo loading of 1.32 wt %) by combining at emplate and pyrolysis strategy.T he Mo-SAC exhibited ab etter HER performance than comparison samples (Mo 2 Cand MoN) in 0.1m KOH. Themost favorable active center,M o 1 N 1 C 2 ,p ossessed the lowest absolute DG H* value (0.082 eV) and the largest DOS near the Fermi level, which was mainly derived from the Mo do rbitals.T he coordination environment of single Mo atoms enhanced the influence of the de lectrons and the HER activity.T his convenient and high-efficiencyd esign was also expanded to Cu, Pd, and Pt active centers.…”

Design aktiver atomarer Zentren für HER‐Elektrokatalysatoren

“…[79] Fürd ie weitere Aufklärung des Mechanismus während des HER-Prozesses in alkalischen Medien ist die Aufzeichnung von Veränderungen der elektronischen Struktur und der Koordinationsumgebung des aktiven Zentrums von zentraler Bedeutung.M ithilfe der Operando-Rçntgenadsorptionsspektroskopie identifizierten Weiu nd Mitarbeiter [182] Materialien auf Molybdänbasis kçnnen nicht nur als Substrate,s ondern auch als aktive Spezies fürd ie HER verwendet werden. [183][184][185] Das rationale Design von effizienten Katalysatoren auf Molybdänbasis und die Erforschung ihrer Aktivitäta uf atomarer Ebene sind jedoch noch immer sehr anspruchsvoll. Erstmals haben wir Molybdän-Einzelatomkatalysatoren (Mo-SAC) auf Stickstoff-dotiertem Kohlenstoff (Mo-Beladung 1.32 Gew.-%) durch eine kombinierte Templat-und Pyrolysestrategie aufgebracht.…”