Reducing the Energy Band Gap of Cobalt Hydroxide Nanosheets with Silver Atoms and Enhancing Their Electrical Conductivity with Silver Nanoparticles

Abstract

Although cobalt hydroxide (Co­(OH)2) has been attracting attention in several applications, its photoelectrochemical property has not yet been fully investigated. In this work, tuning the energy band gap of Co­(OH)2 nanosheets with silver atoms and enhancing their electrical conductivity with silver nanoparticles were then focused. A Ag-doped α-Co­(OH)2 thin film was successfully synthesized via an electrodeposition method. The optical properties of the as-prepared materials were characterized by UV–vis and fluorescence lifetime spectroscopies and further confirmed by density functional theoretical calculation. It was found that Ag atoms between adjacent layers of Co­(OH)2 can reduce its electronic band gap to 2.45 eV (α-Co­(OH)2) as compared to 2.85 eV of β-Co­(OH)2. In terms of electrochemical properties, silver nanoparticles (AgNPs) can enhance the electrical conductivity of Co­(OH)2 nanosheets, leading to faster charge transfer reducing the internal resistance and significantly increasing the overall charge storage performance. Interestingly, under light illumination, Ag-doped α-Co­(OH)2 exhibits ca. 0.8 times lower charge storage capacity as compared to that under the dark condition. This is because the photoelectrons can be recombined with the generated holes in the conduction band. The charge storage mechanisms of Ag-doped α-Co­(OH)2 operated under dark conditions and light irradiation were further studied and confirmed using in situ electrochemical X-ray absorption spectroscopy (XAS). Overall, the in situ XAS supports the electrochemical result. This finding may pave a way to further develop photoactive advanced functional materials of metal hydroxides and oxides.

Studying charge-carrier intercalation/deintercalation in energy storage materials by optical spectroscopy

“…is a schematic diagram of the energy bands obtained by XPS and UV-vis tests.The calculated VB, CB and Eg of pristine Co(OH)2 are -5.69, -2.84, and 2.85 eV, which are in line with the existing research results36,37 . For discharged Co(OH)2 electrode, with the adsorption (or chemical reaction) of 𝑂𝑂𝑂𝑂 − ions with Co(OH)2 particles, the calculated VB increased to -4.81 eV.…”

Controlling Size Distribution of Silver Nanoparticles using Natural Reducing Agents in MCM‐41@Ag

“…If the charge of the silver is positive, its interaction is electrostatic with the hydroxyl group (OH) due to its negative charge. This effect diminishes the bandgap energy as reported [51] …”

“…This effect diminishes the bandgap energy as reported. [51] Thickness determination of MCM-41@Ag film Figure 8 is a topographic AFM image of a homogenous MCM-41@Ag (Sample 16) thin film deposited on top of a silicon surface. According to the profilometer analysis, the spin-coating technique's average thickness of two layers of deposited material is approximately 23 nm.…”

Effects of Group IB Metals of Au/Ag/Cu on Boosting Oxygen Evolution Reaction of Cobalt Hydroxide

“…From the Mott‐Schottky curves (Figure 5a), it can be seen that Ag−Co(OH) 2 (k=−0.48×10 5 ), Au−Co(OH) 2 (k=−0.69×10 5 ) and Cu−Co(OH) 2 (k=−1.0×10 5 ) catalysts have smaller tangent slope than that of Co(OH) 2 (k=−1.79×10 5 ), and the carrier concentrations are in the order of Ag−Co(OH) 2 >Au−Co(OH) 2 >Cu−Co(OH) 2 >Co(OH) 2 , indicating the improvement of the overall conductivity of the M−Co(OH) 2 catalysts, which also proves that the M−Co(OH) 2 heterostructure has faster charge transfer. In addition, Ag metals can reduce the internal resistance and improve the overall electrical conductivity, thus speeding up the charge transfer during the OER process [52] …”

“…From the Mott-Schottky curves (Figure 5a), it can be seen that AgÀ Co(OH) 2 (k = À 0. reduce the internal resistance and improve the overall electrical conductivity, thus speeding up the charge transfer during the OER process. [52] LSV curves normalized by ECSA verify the intrinsic activity of OER. As shown in Figure 5b, the AgÀ Co(OH) 2 catalyst displays the greatest current density at each potential value, which confirms the high intrinsic activity of the AgÀ Co(OH) 2 catalyst.…”