Mechanistic Study of Controlled Zinc Electrodeposition Behaviors Facilitated by Nanoscale Electrolyte Additives at the Electrode Interface

Abstract

Nanoparticle organic hybrid materials (NOHMs) are liquid-like materials composed of an inorganic core to which a polymeric canopy is ionically tethered. NOHMs have unique properties including negligible vapor pressure, high oxidative thermal stability, and the ability to bind to reactive species of interest due to the tunability of their polymeric canopy. This makes them promising multifunctional materials for a wide range of energy and environmental technologies, including electrolyte additives for electrochemical energy storage (e.g., flow batteries) and the electrochemical conversion of CO2 to chemicals and fuels. Due to their unique transport behaviors in fluid systems, an understanding of the near-electrode surface behavior of NOHMs in electrolyte solutions and their effect on electrochemical reactions is still lacking. In this work, the complexation of zinc (Zn) by NOHMs with an ionically tethered polyetheramine canopy (HPE) (NOHM-I-HPE) was studied using attenuated total reflectance Fourier transform infrared and Carbon-13 nuclear magnetic resonance spectroscopy. Additionally, various electrochemical techniques were employed to discern the role of NOHM-I-HPE during zinc electrodeposition, and the results were compared to those of the electrochemical system containing untethered HPE polymers. Our findings confirmed that NOHM-I-HPE and HPE reversibly complex zinc in the aqueous electrolyte. NOHM-I-HPE and HPE were found to block some of the electrode active sites, reducing the overall current density during electrodeposition, while facilitating the formation of smooth zinc deposits, as revealed by surface imaging and diffraction techniques. Observed variations in the current density responses and the degree of passivation created by the NOHM-I-HPE and HPE adsorbed on the electrode surface revealed that their different packing behaviors at the electrode–electrolyte interface influence the zinc deposition mechanism. The presence of the nanoparticle and ordering offered by the NOHMs as well as the structured conformation of the polymeric canopy allowed the formation of void spaces and free volumes for enhanced transport behaviors. These findings provided insights into how structured electrolyte additives such as NOHMs can allow for advancements in electrolyte design for controlled deposition of metal species from energy-dense electrolytes or for other electrochemical reactions.

Impacts of Bond Type and Grafting Density on the Thermal, Structural, and Transport Behaviors of Nanoparticle Organic Hybrid Materials‐Based Electrolytes

“…[27,33,37,39,40,[44][45][46][47][48] Moreover, the multitude of combinations of polymers [33] , linkers [32,33] , and nanoparticles [49] in NOHMs makes this class of materials especially desirable for applications such as integrated CO 2 capture and conversion systems [10,28] and redox flow batteries. [9,50] For example, the strategic selection of polymers with specific functional groups can optimize the binding energy for target species including small gaseous (e.g., CO 2 ) or ionic species (e.g., Cu +2 , Zn +2 ). Though NOHMs synthesized with an ionic bond have been shown to be ionically conductive, they are challenged by high viscosity [31,34,51] and thus would need to be incorporated into electrolytes as additives.…”

Enhancing the Performance of Reversible Zn Deposition by Ultrathin Polyelectrolyte Coatings

“…Figure shows the obtained current transient during Zn electrodeposition at a potential of −1.255 V (vs Ag/AgCl). The current response exhibits three distinct features corresponding to nucleation and growth during Zn electrodeposition. − Initially, the current increases due to an increase in the active surface area of the electrode caused by the growth of Zn crystals. After a certain period ( t max ), the current density reaches its maximum value ( j max ) when the nucleation sites have grown sufficiently large, resulting in the overlapping of diffusion zones as predicted by the Avrami theorem.…”

From Ionic Nanoparticle Organic Hybrids to Ionic Nanocomposites: Structure, Dynamics, and Properties: A Review

“…Jeffamine (M-2070) canopies were tethered to SiO nanocores via ionic bonding. It was shown by small-angle neutron scattering (SANS) that tethered, interacting, or free polymers were present in aqueous solutions of such nanoparticle organic hybrids [ 52 , 53 , 54 ]. A large portion of free polymers appeared in the solution and were not bound to the functionalized nanosilicas [ 53 ].…”

“…The cation of the electrolyte competed with the amine of the tethered polymer (canopy), replacing the tethered polymer and, thus, causing the detachment of the canopy from the nanoparticle surface [ 53 ]. For instance, zinc (Zn ) has a low binding energy with the ether oxygen of Jeffamine, which allows the movement of “free” Zn from the bulk to the surface [ 54 ]. Moreover, nanosilica modified with coronas were implemented to decorate cotton fibers using electrostatic interaction.…”