Metal–Organic Framework‐Derived Hollow CoS_x Nanoarray Coupled with NiFe Layered Double Hydroxides as Efficient Bifunctional Electrocatalyst for Overall Water Splitting

Abstract

First-row transition metal-based catalysts, such as metal oxides, sulfides, selenides, phosphides, and hydroxides of Co, Ni, Fe, and Mo have been studied intensively owing to high intrinsic activities and low cost. [9,10] However, most of the reported catalysts exhibited satisfactory activity and stability toward either HER or OER, which complicates the configuration of an integrated electrolyzer. [11] To simplify the system and reduce the overall cost for industrial applications, a transition metalbased bifunctional electrocatalyst that can catalyze both the HER and OER process is essential.Ni-Fe based layered double hydroxides (NiFe LDHs) are considered to be competitive OER catalyst candidates in alkaline media. [12,13] In contrast, the catalytic performance of NiFe LDHs in HER is unsatisfactory owing to the sluggish HER kinetics resulting from a large energy barrier for the Volmer step. [14,15] Additionally, NiFe LDHs suffer from the inherent problems associated with LDH-based catalysts, such as poor stability caused by self-aggregation and a low electrochemically-active surface area. [16,17] Therefore, the design of NiFe-based LDHs, with improved HER catalytic properties and maintained OER performance, to serve as effective bifunctional catalysts for electrolysis of water is an important challenge. In this regard, the controlled integration of NiFe LDHs and HERactive catalysts into a hetero-nanostructure may be a reasonable strategy to fabricate highly efficient bifunctional catalysts for water splitting. [18] Because of their high surface area and open structure, hollow-structured HER catalysts are believed to be ideal templates for NiFe LDH growth. [19,20] Previous studies have confirmed that growing LDHs on hollow-structured HER catalysts can increase the electrochemically-active surface area and inhibit self-aggregation of LDHs. [21] Recently, metal-organic frameworks (MOFs) have been considered as efficient precursors for fabricating porous and/ or hollow-structured materials based on their tunable physicochemical properties. [22,23] Consequently, numerous research groups have attempted to develop MOF-derived hollow-structured materials as highly efficient electrocatalysts for the HER process. [24,25] For example, Wang et al. fabricated a Ni-Co bimetallic sulfide catalyst with a multi-shell hollow structure (derived from the MOF component of the catalyst) for enhanced HER For effective hydrogen production by water splitting, it is essential to develop earth-abundant, highly efficient, and durable electrocatalysts. Herein, the authors report a bifunctional electrocatalyst composed of hollow CoS x and Ni-Fe based layered double hydroxide (NiFe LDH) nanosheets for efficient overall water splitting (OWS). The optimized heterostructure is obtained by the electrodeposition of NiFe LDH nanosheets on metal-organic framework-derived hollow CoS x nanoarrays, which are supported on nickel foam (H-CoS x @NiFe LDH/NF). The unique structure of the hybrid material not only provides ample active sites, but also facilit...

Hollow Mo-doped NiSx nanoarrays decorated with NiFe layered double-hydroxides for efficient and stable overall water splitting

“…S10 †). 9 Besides, no lattice fringes corresponding to the MoS x structure are observed, revealing successful incorporation of Mo species into the structure of NiS x without generating any new crystalline phase, which coincides well with the XRD result. The TEM images of HAADF-STEM and element mapping of the Mo-NiS x @NiFe LDH/NF demonstrate that Ni, Fe, Mo, O and S elements are successfully detected on the surface of the entire structure (Fig.…”

“…5,6 Water electrolysis comprises two half-reactions, the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), 7,8 but the high potential and slow kinetics of the OER reduce the overall efficiency of water splitting, which encourages us to design more HER/OER catalysts with low overpotential. 9 Currently, noble metal Pt-based and RuO 2 /IrO 2 catalysts have been considered as the cutting-edge electrocatalysts for the HER and OER, respectively. 10 However, resource scarcity and instability seriously limit their massive industrialization.…”

“…24,25 In particular, hollow-structures could simultaneously enhance intrinsic activity and achieve increased active sites to synergistically optimize the electrocatalytic property. [26][27][28] For example, Park et al 9 designed a hollow H-CoS x and NiFe LDH nanosheet hybrid material used as a bifunctional electrocatalyst for water electrolysis. Feng et al 29 synthesized a novel cactus-like NiCo 2 S 4 @NiFe LDH for both the oxygen reduction reaction (ORR) and OER.…”

Anchoring Co3S4 nanowires on NiCo2O4 nanosheet arrays as high-performance electrocatalyst for hydrogen and oxygen evolution

“…From the TEM images, it can be seen that there are two struc- The above results reveal that there is strong electron interaction between Co, Fe, S and O after the formation of the heterostructure at the NiCo 2 O 4 / Co 3 S 4 heterostructure interface, and the potential interfacial electronic structure reconfiguration will be benefit to promote the electrocatalytic activity during water splitting. [46][47][48][49][50][51][52] After understanding the composition and structure of the catalysts, electrocatalytic activity of the catalysts was further analyzed. The HER performance of the catalysts was assessed in KOH (1 M) solution.…”

MOF-derived nanoarrays as advanced electrocatalysts for water splitting

“…12b). 128 Afterwards, NiFe LDH nanosheets were deposited Reproduced with permission. 126 Copyright 2020, Wiley-VCH.…”