I am trying to characterize an electrochromic system. The system uses ITO electrodes on glass, WO3 as the electrochromic film, and NiO as the ion storage layer. When I deposit NiO and WO3 and take the CV in a three electrode potentiostat system, the colour changes and the CV is good. However, when I use an LITFSI in EMI-TFSI electrolyte with PMMA electrolyte and form an electrochromic device with a 2 electrode setup (the counter and reference electrodes are connected together) in my potentiostat, it does not work. The colour does not change and the CV shows either zero current or behaves like a resistor with a constant linear slope. Does anyone have any ideas on why the films work but the device does not?
The working electrode must be polarized at a specific potential to obtain the electrochromic effect. It is an easy task in a 3 electrodes cell.
In a 2 electrodes experiment a voltage is applied, without any control on the WORK electrode potential . Can you introduce a REF electrode in the second cell?
The ion transfer should be very low[1,2], in the 2nd case ('device'), maybe due to some very high cycling(?) history, or out of specs conditions of storage (or long calendar time?) aging of this (nominally electrochromic) device.
You will get your own ideas, if you could measure Electrochemical Impedance Spectroscopy (EIS)[2,3] of 'this device'; it would be, even better, if you could measure (P-)EIS[4] for both cells, then you find a very helpful comparison tool of their ion transfer rate(s).
1. Rate limiting activity of charge transfer during lithiation from ionic liquids https://www.sciencedirect.com/science/article/abs/pii/S0378775316311399
2. Electrochemical Impedance Spectroscopy at Redox-Type Liquid|Liquid Interfaces: The Capacitance Lag https://pubs.acs.org/doi/10.1021/acs.jpcc.9b10116
3. see Figure S6 (charge transfer) in: Charge-transfer complexes for solid-state Li+ conduction https://pubs.acs.org/doi/suppl/10.1021/acsaelm.0c00393/suppl_file/el0c00393_si_001.pdf
4. Set the parameter V.dc, the DC (V-)polarization value, from the equation: V.dc ~= (V.high-V.low)/2, in the new(er) P-EIS measurements; get the V.high and V.low values, from your (previous) CV- limits.
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