A Heterostructure Coupling of Exfoliated Ni–Fe Hydroxide Nanosheet and Defective Graphene as a Bifunctional Electrocatalyst for Overall Water Splitting

Abstract

Herein, the authors demonstrate a heterostructured NiFe LDH-NS@DG10 hybrid catalyst by coupling of exfoliated Ni-Fe layered double hydroxide (LDH) nanosheet (NS) and defective graphene (DG). The catalyst has exhibited extremely high electrocatalytic activity for oxygen evolution reaction (OER) in an alkaline solution with an overpotential of 0.21 V at a current density of 10 mA cm , which is comparable to the current record (≈0.20 V in Fe-Co-Ni metal-oxide-film system) and superior to all other non-noble metal catalysts. Also, it possesses outstanding kinetics (Tafel slope of 52 mV dec ) for the reaction. Interestingly, the NiFe LDH-NS@DG10 hybrid has also exhibited the high hydrogen evolution reaction (HER) performance in an alkaline solution (with an overpotential of 115 mV by 2 mg cm loading at a current density of 20 mA cm ) in contrast to barely HER activity for NiFe LDH-NS itself. As a result, the bifunctional catalyst the authors developed can achieve a current density of 20 mA cm by a voltage of only 1.5 V, which is also a record for the overall water splitting. Density functional theory calculation reveals that the synergetic effects of highly exposed 3d transition metal atoms and carbon defects are essential for the bifunctional activity for OER and HER.

Single‐Atom to Single‐Atom Grafting of Pt1 onto FeN4 Center: Pt1@FeNC Multifunctional Electrocatalyst with Significantly Enhanced Properties

“…One is the synergistic catalysis among the heteroatoms of active moiety that is similar to its function to HER. [23,45] The other is associated with the low coordinated dangling Pt 4+ atoms that may facilitate the H 2 O adsorption and promote OER, although metallic Pt NPs are not active to OER. [22,46] In addition, the overvoltage (ΔE = E j = 10 −E 1/2 ) between OER and ORR, which is used to evaluate the reversibility of oxygen electrodes, is 0.67 V for Pt 1 @FeNC, much lower than that of the recently reported highly active NPMCs, precious metal, and metal-free catalysts, e.g., Co@Co 3 O 4 / NC (0.85 V), [47] Fe@N-C-700 (0.88 V), [48] 20 wt% PtRu/C (0.88 V), [49] S-doped CNTs (0.79 V).…”

“…[22] The synergy between hetero-components or -structures has also been proved as the key factor for high OER/HER activities. [23] Recently, the single-atom catalysts (SACs) have attracted much attention for electrocatalysis applications because of their unique properties such as the maximized atom utilization, high catalytic activity, and selectivity. [24][25][26] Since the active sites of FeNC catalysts are atomically dispersed atoms, it is believed that the modulation to these active atoms may take the advantage of SACs and change the catalysis behavior of FeNC for energy conversion and storage reactions.…”

A highly-efficient oxygen evolution electrode based on defective nickel-iron layered double hydroxide

“…Dai's group [34] has anchored NiFe LDHs on conductive carbon nanotube to enhance the conductivity, thus improving their OER activity with an early onset potential of 1.45 V. Luo et al [35] intercalated phosphorus oxoanions into NiFe LDHs to tune the surface electronic structure, and 1.45 V was also obtained for the onset potential. Moreover, by combining the abovementioned methods, the OER onset potential of NiFe LDH can be much improved, but still larger than 1.40 V so far [36]. On the other hand, exfoliation of NiFe LDH/ engineering the nanostructure commonly involved var-ious organic solvents or harsh conditions like high temperature/pressure.…”

Hierarchical Hollow Nanoprisms Based on Ultrathin Ni‐Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution

“…Figure 4a presents the iR-compensated (see the Experimental Section in the Supporting Information for details) polarization curve.Aredox peak was observed at around 1.4 V relative to the reversible hydrogen electrode (RHE), which was assigned to the oxidation of Ni 2+ to Ni 3+ . [23,49] ForO ER performance evaluation, the operating potentials required for acurrent density (j)o f1 0mAcm À2 are usually compared. In the present case,a na nodic electrode based on the hierarchical hollow nanoprisms required as mall potential of 1.51 V (vs.R HE) to generate a j value of 10 mA cm À2 ,w hich corresponds to al ow h value of 280 mV.F or comparison, the polarization curves of the control samples with iR correction were also investigated ( Figure S9).…”

“…[20] Theh igh electrocatalytic activity of the Ni-Fe LDH hollow nanoprisms compares favorably with those of many high-performance Ni-FeL DH based electrocatalysts (Table S1). [20,21,23,25,27,49,50] Thee nhanced performance might be ascribed to their unique hollow features and optimized chemical composition. Specifically,aside from the synergistic effect between Ni and Fe,the hierarchical hollow nanoprisms with large surface areas could provide sufficient electroactive sites for electrocatalytic reactions.A si ndicated by the cyclic voltammograms (CVs) in ap roper potential range without redox processes and the corresponding capacitive current plots against the scan rate,the Ni-FeLDH hollow nanoprism sample has amuch larger double-layer capacitance (C dl )than the Ni-FeL DH nanocluster catalyst, demonstrating that the larger electrochemically active surface area (ECSA) of the hollow structure might be responsible for the enhanced OER performance ( Figure S10).…”