Dedicated for Wolfgang Schuhmannonthe occasion of his 60 th birthday 1Introduction Research in the fieldo fm aterials engineering has led to advances in hydrogel science and technology leading to aw ide spectrum of applications in biomedicine [1],a griculture [2],t issue engineering [3],a quaculture [4],i nfant care [5],e lectrochemistry[ 6] and nanotechnology [7].Hydrogels can have various physicalf orms,s tarting from solid powders,m icroparticles,f ilms or membranes up to solid or liquid capsules.T heya re made of polymer chains interconnected in various mannert hus forming 3D cross-linked structures known as polymer networks.H owever,t he main component of hydrogel is water constituting 40 %t o9 9% of itst otal mass [8].T hey can be produced usingm any different methods,w hile chemically cross-linked hydrogels exhibit higher thermal and chemical resistance in comparison with ones obtainedb ym eans of physical cross-linking [9].In the last decade,u tilization of as olid-state electrolyte containing ah ydrogel has been considered as as ubstitute of al iquid electrolyte for different electrochemical devices [10].H oweverl iquid electrolytes have high ionic conductivity,t hus allowing quick ion migration between the electrodes which enables obtaining electricity that can be obtained and stored in form of chemical power source. Nevertheless,t hey have also numerous disadvantages. Using liquid electrolyte can be dangerousb oth for its direct user, as well as for the environment. Hazard of www.electroanalysis.wiley-vch.de