In Situ Enhancement of Flow-through Porous Electrodes with Carbon Nanotubes via Flowing Deposition

Maximizing the power density of aqueous electrochemical flow cells with in operando deposition

“…When multiplied by the flow rate through the electrode this leads to a maximum total pumping power consumption of 0.05 mW. Although this value is considerably higher than for the previous deposition method [18], it is negligible (<0.1%) when compared to the power output of the cell and indicates a general decrease in electrode pore size distribution. In addition, the pressure pulsations due to the 'logjam' effect can also be observed in the potentiostatic measurements as a regular pulsation in the output current, as shown in Fig.…”

“…Using the flowing deposition method recently invented by our group, carbon nanotubes (CNTs) are deposited at the upstream entrance and within the porous carbon paper. As explained in the previous study [18] and depicted in Fig. 3, the CNTs form a nanoporous layer with a much greater surface area per volume than the carbon paper scaffold.…”

“…Flowing deposition of a temporary dilute suspension of CNTs in deionized water is accomplished with the same injection and rinsing method previously reported [18], whereas CNTs are dispersed directly into the reactants for dynamic in operando flowing deposition.…”

“…An investigation into the ionic conductivity of the electrolytes, discussed in section S1 of the electronic supplementary information (ESI) and displayed in Table S2-1 and S2-2 of the ESI, indicate that volumetric power density can best be enhanced by decreasing the width of the centre channel. Although larger electrode width also has a positive effect on power output through both decreased electrical resistance and increased electrochemical surface area (ESA), these effects can be better improved through the use of current collectors [23] and surface area enhancement, respectively [18]. In addition to architectural modifications, the investigation into ionic conductivity also reveals that changes in electrolyte formulation can further decrease the ohmic resistance of the centre channel.…”

“…This is accomplished by simultaneously addressing all three sources of voltage loss in electrochemical cells, namely those due to kinetic, ohmic and mass transport constraints. The inspiration for this endeavour stems from the promising preliminary results observed with the in situ flowing deposition method recently invented by our group whereby a temporary suspension of carbon nanotubes (CNTs) is injected through an assembled flow cell before operation in order to increase the surface area of the pre-existing carbon paper electrode by over an order of magnitude [18]. In the present work, it is further shown that this flowing deposition can be achieved dynamically during operation of a flow cell, leading to even higher surface area and better mass transport characteristics [19].…”