Interface Properties of 2D Graphene–Polydopamine Composite Electrodes in Protic Ionic Liquid-Based Electrolytes Explored by Advanced Electrogravimetry

Abstract

A fundamental understanding of the processes occurring at the electrode/electrolyte interfaces is of paramount importance to enhance the performance of energy storage devices. Addressing this issue requires suitable characterization tools, due to the complex nature of such interfaces. By means of electrochemical quartz crystal microbalance (EQCM) and its advanced mode, the so-called ac-electrogravimetry, herein, we report on the interfacial properties of two-dimensional (2D) graphene−polydopamine (ERGO-PDA) composite electrodes in diverse electrolyte compositions including a protic ionic liquid (PIL), pyrrolidinium hydrogen sulfate [Pyr + ][HSO 4 − ]. We have performed a comparative study in a [Pyr + ]-[HSO 4 − ]−water binary mixture in the absence and presence of Na 2 SO 4 and compared it with the interfacial behavior of ERGO-PDA in a 0.5 M Na 2 SO 4 (pH = 2) pristine electrolyte. Our EQCM and ac-electrogravimetric analyses reveal that the [Pyr + ] ions, due to their chaotropic nature, inhibit the approach of kosmotropic Na + ions and water molecules to the interface, suppressing the contribution of electrodragged water molecules, substantially observed in the case of pristine aqueous electrolyte. Despite the dissimilarity of the charge compensation process occurring in the presence of [Pyr + ][HSO 4 − ], the ERGO-PDA electrode is able to maintain similar cycling stability (99% for 10,000 cycles at 1000 mV•s −1 ) and specific capacitance values (325 F•cm −3 ) compared with the pristine aqueous electrolyte, with the advantage of superior energy density (16.3 versus 8.7 mWh•cm −3 ) due to a noticeably enlarged potential window in [Pyr + ][HSO 4 − ]−water binary mixtures.

Hydrothermal Synthesis of a Graphene‐based Composite Enabling the Fabrication of a Current Collector‐free Microsupercapacitor with Improved Energy Storage Performance

“…Free H 2 O molecules were detected at intermediate frequencies. The transfer order of the two cations as well as the participation of free water is consistent with ac‐ electrogravimetry measurements previously performed on carbon materials in similar electrolytes [28–31] …”

“…The transfer order of the two cations as well as the participation of free water is consistent with ac-electrogravimetry measurements previously performed on carbon materials in similar electrolytes. [28][29][30][31] The interfacial transfer constants, Ki, of the different species involved in the charge compensation process as a function of the applied potential for rGO and rGO-PDA are shown in Figure S4. From this figure, it is clear that the three exchanged species transfer faster at the composite electrode interface, rGO-PDA, compared to that at the rGO.…”

Highly Ordered Graphene Polydopamine Composite Allowing Fast Motion of Cations: Toward a High‐Performance Microsupercapacitor

“…Indeed, in a protic ionic liquid, pyrrolidinium hydrogen sulfate [Pyr + ][HSO 4 − ], no water transfer was detected. [ 32 ] From the relative concentration changes ( C i – C 0 ) values, the corresponding mass variations of each species can be obtained with consideration of their molar masses ( M i ) (Figures S8B and S9C, Supporting Information). The global mass response can be recalculated from ac‐electrogravimetry by the addition of individual mass ( Δm i ) of the three species detected by ac‐electrogravimetry.…”

Supramolecular temperature responsive assembly of polydopamine reduced graphene oxide

“…Such temperature responsive materials could be helpful in applications including catalysis, 71 sensors, 72 lubrication, 73 anticorrosion coatings, 74 pollutant removal, 75 actuators, 76 and energy storage. 77 Since PDA can bind onto virtually any material, a similar strategy may potentially be adapted and extended to other hydrophobic nanomaterials (e.g., carbon nanotubes, boron nitride flakes) to form PDA clusters that would impart amphiphilicity to the resulting composites. This in turn would enable STRAN, allowing to control the properties of both suspensions and resulting solid materials.…”