Sequential Capacitive Deposition of Ionic Liquids for Conformal Thin Film Coatings on Oxygen Reduction Reaction Electrocatalysts

Abstract

Ionic liquid (IL)-modified carbon-supported catalysts have demonstrated significant improvements in oxygen reduction reaction (ORR) activity. However, transition of this result from the half-cell to the proton exchange membrane fuel cell (PEMFC) has been challenging. Presented here is a processing methodology that yields the formation of a thin (<2 nm) conformal IL coating on the surface of both three-dimensional electrocatalysts and bulk single crystals through the sequential capacitive deposition (SCD) of anionic and cationic components and their subsequent condensation into a hydrophobic, protic IL. SCD shows promise for IL incorporation into preformed PEMFC catalyst layers.

Emerging Applications of Solid Catalysts with Ionic Liquid Layer Concept in Electrocatalysis

“…studied the stability performance of Pt/C catalysts with and without an thin film coating of IL ([MTBD][BETI]), and also observed that the IL‐coated Pt/C suffered from much less significant loss in both ECSA and ORR activity in 0.1 m HClO 4 after potential cycling for up to 10 000 cycles with different upper potential limits (Figure 11g, 12h). [ 101 ]…”

“…Most recently, Snyder et al reported a unique sequential capacitive deposition method to introduce IL molecules onto Pt/C catalyst, which was implemented through sequential exposure of the catalyst coated RDE electrode to electrolytes containing either the anion or cation under positive or negative potentials. [101] Thereby, the double layer capacitive charging acts to pull the ions, resulting in formation of a thin conformal layer of the desired IL within the catalyst. The as-prepared IL modified catalysts can also exhibit enhanced ORR activity and stability in 0.1 m HClO 4 .…”

“…[105] More recently, Snyder et al studied the stability performance of Pt/C catalysts with and without an thin film coating of IL ([MTBD][BETI]), and also observed that the IL-coated Pt/C suffered from much less significant loss in both ECSA and ORR activity in 0.1 m HClO 4 after potential cycling for up to 10 000 cycles with different upper potential limits (Figure 11g, 12h). [101] It is generally accepted that the improved electrochemical stability of Pt-based catalysts after IL modification can arise from reduced Pt dissolution, lower degree of Pt particle agglomeration or suppressed carbon corrosion. [103] To unambiguously explore the working mechanisms of ILs in stabilizing Pt-based ORR catalysts, Etzold et al studied the electrochemical stability of a series of Pt/C catalysts modified with imidazolium-based ILs using combined identical location transmission electron microscopy (TEM) and in situ scanning flow cell coupling to an inductively coupled plasma mass spectrometer (SFC-ICP-MS) analyses (Figure 12).…”

<i>Operando</i> X-ray Absorption Spectroscopic Study on the Effect of Ionic Liquid Coverage upon the Oxygen Reduction Reaction Activity of Pd-core Pt-shell Catalysts

“…[23][24][25] Many groups have investigated the ability of IL modifications to enhance ORR activity with a variety of IL. [26][27][28] Snyder et al firstly reported the development of a new architecture in which high surface area and nanoporous Ni-Pt alloy nanoparticles encapsulated with a hydrophobic [7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD)][bis(pentafluoroethylsulfonyl)imide (BETI)] IL. 23 The ORR activity of this porous PtNi was improved 2-3 times after IL modification; the resultant activity was nearly an order of magnitude higher than that of commercial Pt/C.…”

Caffeinated Interfaces Enhance Alkaline Hydrogen Electrocatalysis

“…Extension of the diffusion limited HOR current density to higher potentials has also been observed for nanoscale catalysts, Pt/C, as shown inFigure S6. The effect of caffeine on OH adsorption is more directly observed by analyzing its effect on reactions where OHad is a demonstrated reactant33 , namely CO oxidation.Figures 2(d) and S7show that caffeine causes a positive shift in the peak and onset potentials for CO bulk oxidation and CO monolayer stripping, respectively.Together, Figures 1, 2 and S7indicate that the presence of caffeine on the surface reduces the coverage of spectator OHad species, either through a physical competition for adsorption sites or through a weakening of the interaction between the Pt surface and OHad. Further work is needed to discern which of these effects is greater.The impact of caffeine on HER/HOR kinetics is surprising and the source of this activity enhancement remains an open question.…”