Liquid Metal Fiber Mat as a Highly Stable Solid-State Junction for Inkjet-Printed Flexible Reference Electrodes

An all-solid liquid-metal-fiber-mat-based membrane flexible reference electrode (LMFM-FRE) was developed by combining liquid metal eutectic gallium indium (EGaIn) and poly(styrene-block-butadiene-block-styrene) (SBS) as a liquid junction layer. Ag ink was printed and chlorinated by electroplating to form the AgCl layer. Then, agarose containing KCl was coated as the electrolyte layer, and LMFM was added as the liquid junction layer. The liquid junction layer can increase the hydrophobicity of the electrode surface, limit the loss of internal Cl^-, and significantly improve the stability of the electrode. The potential fluctuation of LMFM-FRE does not exceed 1 mV within 1 h, and it is still the same after 1 month. In addition, its potential changes in ion species and concentration, pH value, and ambient light are small, and its cyclic voltammetry characteristics are consistent with the standard reference electrode. Even in the case of temperature change and mechanical deformation, the potential change of LMFM-FRE is minimal. In general, the materials used and fabrication by inkjet printing make it possible to manufacture the reference electrode on a large scale, which is particularly important in many electrochemical sensing fields.