Reference electrode
The present disclosure provides for a coated, substrate for use as an electrode, the coated substrate comprising a substrate that is at least partially coated with a layer comprising a polymer and a redox active substance, wherein the polymer is a cation exchange polymer, and wherein the redox active substance is present in both an oxidised and reduced state. A method for making the isolated coated substrate, and an electrochemical apparatus using the electrode as a reference electrode, is also discussed herein.
1 . A coated, isolated substrate for use as an electrode, the coated isolated substrate comprising a substrate that is at least partially coated with a layer comprising a polymer and a redox active substance,
wherein the polymer is a cation exchange polymer,
wherein the redox active substance is present in both an oxidised and reduced state, and
wherein the maximum dimension of the substrate is less than 1 mm.
2 . The substrate according to claim 1 , wherein the substrate is isolated from an electrochemical circuit.
3 . The substrate according to claim 1 , wherein a) the layer comprises a film of the polymer with the redox active substance dispersed in the polymer, or b) the layer comprises a plurality of particles comprising the polymer and the redox active substance.
4 . The substrate according to claim 1 , wherein the layer comprising a polymer and redox active substance has a thickness of from 3 μm to 100 μm.
5 . The substrate according to claim 1 , wherein both the reduced redox active substance and the oxidised redox active substance are distributed homogenously in the polymer.
6 . The substrate according to claim 1 , wherein the cation exchange polymer is formed from a perfluorinated monomer and a monomer having sulfonate groups.
7 . The substrate according to claim 6 , wherein the molar ratio of redox active substance to cation exchange sites in the polymer is from 10:1 to 150:1.
8 . The substrate according to claim 1 , wherein the molar ratio of the oxidised redox active substance to the reduced redox active substance is from 1:1500 to 1500:1.
9 . The substrate according to claim 1 , wherein at least one of the reduced redox active substance or the oxidised redox active substance is positively charged or insoluble in water.
10 . The substrate according to claim 1 , wherein at least one of the reduced redox active substance or the oxidised redox active substance has a diffusion coefficient in the polymer of greater than 1×10 −10 cm 2 s −1 .
11 . The substrate according to claim 1 , wherein the redox active substance comprises a species selected from a metallocene, an organic cation, or a metal complex.
12 . The substrate according claim 11 , wherein the reduced redox active substance comprises a ferrocene and the oxidised redox active substance comprises a ferrocenium ion.
13 . The substrate according to claim 11 , wherein the redox active substance comprises a bipyridinium compound, wherein the reduced redox active substance has a charge of +1 and the oxidised redox active substance has a charge of +2.
14 . The substrate according to claim 11 , wherein the redox active substance comprises a metal complex, wherein the metal complex comprises a metal and one or more ligands of the formula [M(L) n ], wherein M is Co, Ru or Os with an oxidation state of +2 in its reduced state and an oxidation state of +3 in its oxidised state, and L is a nitrogen-containing heterocycle.