Deconvoluting and Quantifying the Real-time Fluxes and Ionic Currents of Various Species Using In Situ Electrochemical Quartz Crystal Microbalance Measurements

Electrochemical quartz crystal microbalance (EQCM) is a powerful technique to screen the gravimetric response of electrochemical electrodes. In this study, a straightforward mathematical method is proposed for extracting and deconvoluting the real-time fluxes and ionic currents of two species based on the EQCM measurement results. We creatively propose the concept of flux cyclic voltammograms (CVs) and ionic current CVs of various species and apply them to the real-time analyses of molecules/ions dynamics. For proof of concept, Ti3C2Tx MXene, a most studied two-dimensional metal carbide, is investigated as a supercapacitor electrode in a 1M H2SO4 electrolyte. The H2O and H+ flux CV plots are highly symmetrical, indicating reversible inserting/deserting species fluxes. The highest fluxes along with maximum hydration numbers are obtained at the peak current potential. This suggests the significant contribution of double-layer capacitance originates from the insertion of hydrated H+. The H+ CV with the ionic current induced by H+ flux overlaps the real CV, confirming that H+ is the only interactive ion for screening the electrode charge. Lastly, we also validate the proposed strategy using Ti3C2Tx MXene electrode in 1M KCl electrolyte and YP80 porous carbon electrode in 1 M LiCl electrolyte.