Surface Modification Approach to TiO₂ Nanofluids with High Particle Concentration, Low Viscosity, and Electrochemical Activity

Abstract

This study presents a new approach to the formulation of functional nanofluids with high solid loading and low viscosity while retaining the surface activity of nanoparticles, in particular, their electrochemical response. The proposed methodology can be applied to a variety of functional nanomaterials and enables exploration of nanofluids as a medium for industrial applications beyond heat transfer fluids, taking advantage of both liquid behavior and functionality of dispersed nanoparticles. The highest particle concentration achievable with pristine 25 nm titania (TiO2) nanoparticles in aqueous electrolytes (pH 11) is 20 wt %, which is limited by particle aggregation and high viscosity. We have developed a scalable one-step surface modification procedure for functionalizing those TiO2 nanoparticles with a monolayer coverage of propyl sulfonate groups, which provides steric and charge-based separation of particles in suspension. Stable nanofluids with TiO2 loadings up to 50 wt % and low viscosity are successfully prepared from surface-modified TiO2 nanoparticles in the same electrolytes. Viscosity and thermal conductivity of the resulting nanofluids are evaluated and compared to nanofluids prepared from pristine nanoparticles. Furthermore, it is demonstrated that the surface-modified titania nanoparticles retain more than 78% of their electrochemical response as compared to that of the pristine material. Potential applications of the proposed nanofluids include, but are not limited to, electrochemical energy storage and catalysis, including photo- and electrocatalysis.

Preparation Techniques of TiO2 Nanofluids and Challenges: A Review

“…Figures 18 and 19 shows the variation in viscosity as a function of temperature and particle concentration [66,67,82,[99][100][101]105,112,117,118], respectively. In Figure 18 the error bars represent the upper and lower values of viscosity with particle concentration at the specific temperature, while in Figure 19 the ends of the bars showed the maximum and minimum values of viscosity with temperature at the specific value of particle concentration, for the particular study.…”

Review Article: Flow battery systems with solid electroactive materials

“…Such modification would be expected to be beneficial to (1) facilitate transport of electrons and ions; and (2) further reduce the suspension viscosity to increase the operating efficiency. 140 Another potential route to improve the system may include designing an innovative flow channel which maximizes the active surface area while minimizing pressure drop. Such a modification to the current collector is important because type III has to be operated such that the flow facilitates contact between active material particles and the current collector.…”

“…311 Anatase TiO 2 is another titanium-based Li-ion anode material with an average potential of $1.8 V versus Li/Li þ and a theoretical capacity of 330 mA h/g, and it has been reported in RFBs. 140,174,312,313 A type IV cell configuration showed $1.25 V versus Li/Li þ discharge voltage for CoCp* 2 and CoCp 2 mediators and using TiO 2 particles as the energy storage material that facilitated chemical redox with the mediators. 174 TiO 2 has cost, environmental, and safety advantages and a high ionic conductivity, but the electronic conductivity and rate capability are low relative to other anode materials.…”

“…125,138,139 Coatings on the carbon particles and suspension additives may provide opportunities to reduce suspension viscosity and/or reduce the total amount of carbon that must be dispersed in the slurry. [140][141][142][143] In addition, there is a tradeoff between the power density and the coulombic efficiency depending on the slurry conductivity. A high conductivity is needed to provide high power density with reasonable overpotential; however, shunt currents will be much more significant with a highly conductive carbon network, resulting in a loss of coulombic efficiency for a system with cells in series.…”

“…% particle loading), and high colloidal stability while maintaining good electrochemical activity. 140 Surface grafting of small organic molecules onto cFe 2 O 3 was used to decrease suspension viscosity significantly, although the electrochemical activity was partially suppressed by the surface grafting. 333 Polyethyleneimine, a cationic surfactant, was found to effectively help disperse LFP and carbon suspensions and improve the homogeneity of LFP-C slurry electrodes, hence improving the electrochemical performance via processing of the slurry electrodes for conventional Li-ion cells.…”