In Situ Cation Intercalation in the Interlayer of Tungsten Sulfide with Overlaying Layered Double Hydroxide in a 2D Heterostructure for Facile Electrochemical Redox Activity

Abstract

The role of electrochemical interfaces in energy conversion and storage is unprecedented and more so the interlayers of two-dimensional (2D) heterostructures, where the physicochemical nature of these interlayers can be adjusted by cation intercalation. We demonstrate in situ intercalation of Ni2+ and Co2+ with similar ionic radii of ∼0.07 nm in the interlayer of 1T-WS2 while electrodepositing NiCo layered double hydroxide (NiCo-LDH) to create a 2D heterostructure. The extent of intercalation varies with the electrodeposition time. Electrodeposition for 90 s results in 22.4-nm-thick heterostructures, and charge transfer ensues from NiCo-LDH to 1T-WS2, which stabilizes the higher oxidation states of Ni and Co. Density functional theory calculations validate the intercalation principle where the intercalated Ni and Co d electrons contribute to the density of states at the Fermi level of 1T-WS2. Water electrolysis is taken as a representative redox process. The 90 s electrodeposited heterostructure needs the relatively lowest overpotentials of 134 ± 14 and 343 ± 4 mV for hydrogen and oxygen evolution reactions, respectively, to achieve a current density of ±10 mA/cm2 along with exceptional durability for 60 h in 1 M potassium hydroxide. The electrochemical parameters are found to correlate with enhanced mass diffusion through the cation and Cl–-intercalated interlayer spacing of 1T-WS2 and the number of active sites. While 1T-WS2 is mostly celebrated as a HER catalyst in an acidic medium, with the help of intercalation chemistry, this work explores an unfound territory of this transition-metal dichalcogenide to catalyze both half-reactions of water electrolysis.

Intra-Lattice Inverse Charge Transfer in Bimetallic Electrocatalysts

“…71 In fact, blessed with easy processability and favorable water adsorption kinetics, LDH analogues are already celebrated as OER electrocatalysts. 9,15,19,[72][73][74][75] The obstacle with LDH catalysts is their low operational stability, but here NMH-24 shows excellent durability for minimum 100h at 20 mA cm -2 albeit a slight change in overpotential occurs at high current density (Figure 4h).…”

“…The Ni foam electrodes of 0.5 × 1 cm 2 area were dipped in an aqueous electrolyte containing 0.48g NiCl2.6H2O, 0.05g (NH4)6Mo7O24 and 0.11g NH4Cl followed by potentiostatic deposition under -1.7 V versus Ag/AgCl for different time periods of 6, 12, 18, 24, 30 min. 9,19 Ni-and Mo-only hydroxides (NH-24 and MH-24) were electrodeposited for 24 min under the same potential taking only Ni-and Mo-salt, respectively.…”

“…Likewise, interfacial electronic distribution during metal-to-metal charge transfer in heterojunctions alters the electron density of metal centers. 8,9 In composites, this can initiate electronic coupling between the components, modulating the metal valence states. 10 For instance, Co is more positive in Co coordinated N-rich Mo5N6, since EN of Co and Mo are 1.88 and 2.16, respectively.…”

“…8 Charge transfer occurs from NiCo-LDH to 1T-WS2 in a 2D heterostructure, since the EN of Co (1.88) and Ni (1.91) are lower than W (2.36). 9 Intermetallic charge transfer often leads to an asymmetric electronic distribution at the catalytically active metal centers, impacting the adsorption and desorption of reaction intermediates. [11][12][13] In addition, the catalyst-support charge transfer interactions also influence the overall reactivity.…”

Comprehensive and High‐throughput Electrolysis of Water and Urea by 3–5 nm Nickel and Copper Coordination Polymers

“…Before recording the electrochemical activity of the catalyst, the catalyst was activated by CV scans at higher oxidation and reduction potentials for few seconds at a scan rate of 100 mV s −1 . LSV curves were recorded at a scan rate of 5 and 10 mV s −1 on Ni foam and CFP, respectively, in order to minimize the capacitive current [56] . All the three electrode measurements for OER and HER are conducted at 1 mV s −1 in backward scan unless specified.…”