Sub‐3 nm Ultrafine Monolayer Layered Double Hydroxide Nanosheets for Electrochemical Water Oxidation

Abstract

of OER, a complex four-electron redox process involving OO bond formation that typically requires a high overpotential. [2] RuO 2 and IrO 2 are currently the stateof-the-art materials for OER, though the high cost and low earth abundance of Ru and Ir motivates the search for low-cost alternatives. Layered double hydroxides (LDHs), due to flexible chemical composition, show great potential in photo/ electrocatalysis. [3] Since the first report of NiFe-LDH-based materials exhibiting high OER activity, [4] much research effort has been directed toward the optimization of the OER activity of LDH materials. Hu and co-worker reported that monolayer NiM-LDH nanosheets (M = Fe, Co, etc.) exhibit efficient performance for water oxidation at low overpotentials (0.3 V at 10 mA m −2 ). [5] CoMn, [6] NiCo, [7] NiCoFe, [8] NiV, [9] and VFebased ultrathin LDH nanosheets also show good performance in OER, and core-shell Cu nanowires@NiFe-LDH nanosheets give excellent overall water splitting activity, [10] all the above mainly due to the high surface area and abundance of active surface sites. [11] However, the LDH nanosheet catalysts reported to date generally possess lateral platelet dimensions greater than 30 nm (Table S1, Supporting Information). These platelets are too large to dramatically improve the catalytic performance due to the limited availability of edge and corner sites that are typically highly reactive sites due to coordinative unsaturation. [12] Ultrafine monolayer LDHs with the lateral size of less than 3 nm containing highly exposed coordinatively unsaturated edge or corner active sites are thus a prized research target, potentially offering large catalytic performance improvements compared to conventional monolayer LDH nanosheets. However, the direct synthesis of ultrafine monolayer LDHs has proved extremely challenging to date, thus the potential of ultrafine monolayer LDHs to enhance catalytic and electrocatalytic applications remains unexplored.Traditionally, LDH nanosheets are synthesized with a lateral size of 30-200 nm and monolayer thicknesses using topdown (including solvent exfoliation [13] and plasma etching [14] ) or bottom-up approaches [5,15] (microemulsion methods [16] and layer growth inhibitors [15c,17] ). Reducing the lateral size further to sub-3 nm is challenging due to rapid crystallization kinetics and/or platelet aggregation. [18] Recently, 7.8 nm LDH nanoclusters containing only several layers were obtained using propylene oxide and acetylacetone as solvents, [19] and some ≈5 nm LDH nanosheets have been reported when LDHs were grown in situ on graphene-based supports. [20] Such approaches This study reports the synthesis of ultrafine NiFe-layered double hydroxide (NiFe-LDH) nanosheets, possessing a size range between 1.5 and 3.0 nm with a thickness of 0.6 nm. Abundant metal and oxygen vacancies impart the ultrafine nanosheets with semi-metallic character, and thus superior charge transfer properties and electrochemical water oxidation performance with overpotentials (η) of 254 mV r...

A Simple Synthetic Strategy toward Defect‐Rich Porous Monolayer NiFe‐Layered Double Hydroxide Nanosheets for Efficient Electrocatalytic Water Oxidation

“…[10] Additionally, many researchers devoted to understand the reaction mechanism and active sites of OER for guiding improved OER catalyst development. [13] However, the ultrasonic exfoliation process used to synthesize the ultrafine NiFe-LDH nanosheets was both timeconsuming (many hours of ultrasonication was required) and low-yielding (<50 mg), limiting the potential of the ultrafine NiFe-LDH nanosheets in "real world" energy applications. [12] Recently, we reported the successful synthesis of ultrafine NiFe-LDH nanosheets with size less than 3.0 nm.…”

Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution over Monolayer Layered Double Hydroxide under Irradiation above 600 nm

“…[19] Them -NiAl-LDH was synthesized via af acile in situ growth method by adding the mixture solution of Ni(NO 3 ) 2 ·6 H 2 O, Al(NO 3 ) 3 ·9 H 2 Oand NaOH drop by drop into aqueous solution with 23 vol %offormamide,as firstly reported by Sun et al [20] As presented in the X-ray diffraction (XRD) patterns (Supporting Information, Figure S1), the series of (00l)peaks of b-NiAl-LDH and f-NiAl-LDH illustrated the typically lamellar stack-up for LDH materials. [22] Tr ansmission electron microscopy (TEM;F igure 1a-c) and scanning electron microscopy (SEM;S upporting Information, Figure S2) images showed that the thickness of b-NiAl-LDH, f-NiAl-LDH, and m-NiAl-LDH decreases from 27 nm, to 5nma nd to 1nm, respectively,accompanied with the lateral size varying from 370 nm to 80 nm and to 30 nm. [22] Tr ansmission electron microscopy (TEM;F igure 1a-c) and scanning electron microscopy (SEM;S upporting Information, Figure S2) images showed that the thickness of b-NiAl-LDH, f-NiAl-LDH, and m-NiAl-LDH decreases from 27 nm, to 5nma nd to 1nm, respectively,accompanied with the lateral size varying from 370 nm to 80 nm and to 30 nm.…”

“…[22] Tr ansmission electron microscopy (TEM;F igure 1a-c) and scanning electron microscopy (SEM;S upporting Information, Figure S2) images showed that the thickness of b-NiAl-LDH, f-NiAl-LDH, and m-NiAl-LDH decreases from 27 nm, to 5nma nd to 1nm, respectively,accompanied with the lateral size varying from 370 nm to 80 nm and to 30 nm. [22] Ther atio of Ni/Al was measured to be around 2.8:1.0 for all three LDHs by the energy-dispersive X-ray spectroscopy (EDX) measurement (Supporting Information, Figure S3). [22] Ther atio of Ni/Al was measured to be around 2.8:1.0 for all three LDHs by the energy-dispersive X-ray spectroscopy (EDX) measurement (Supporting Information, Figure S3).…”

Iron–Salen Complex and Co2+ Ion‐Derived Cobalt–Iron Hydroxide/Carbon Nanohybrid as an Efficient Oxygen Evolution Electrocatalyst

“…[1][2][3][4][5][6] Since the efficiency of overall water splitting is restricted by the sluggish kinetics of oxygen evolution reaction (OER) due to multiple proton/ electron transfer processes, [7][8][9] it is important to develop efficient OER electrocatalysts with low overpotential and high durability. [1][2][3][4][5][6] Since the efficiency of overall water splitting is restricted by the sluggish kinetics of oxygen evolution reaction (OER) due to multiple proton/ electron transfer processes, [7][8][9] it is important to develop efficient OER electrocatalysts with low overpotential and high durability.…”

“…[30,31] The harsh conditions used for carbonization of the porous coordination polymers like MOFs, in principle, could be avoided by using molecular complexes with discrete structures as the precursors. [1][2][3][4][5][6] Since the efficiency of overall water splitting is restricted by the sluggish kinetics of oxygen evolution reaction (OER) due to multiple proton/ electron transfer processes, [7][8][9] it is important to develop efficient OER electrocatalysts with low overpotential and high durability. [32] In that study, Xu and co-workers described an in situ formed OER electrocatalyst consisting of interconnected NiFe-LDH and carbon nanodomains by solvothermal reaction of Ni 2+ , Fe 3+ , and 2-mercapto-5-nitrobenzimidazole (MNBI) in N,N-dimethylformamide (DMF).…”