Silver nanoparticles were formed electrochemically in the presence of poly(N-vinylpyrrolidone) (PVP) to generate highly stable nanoparticles with a mean diameter of 12 nm. The optimised conditions involved formation at − 6.0 V vs Ag|Ag+ with a PVP:Ag+ ratio of 75:1. Particle agglomeration was observed when the PVP:Ag+ ratio was reduced to 25:1 and when extended polarisation periods were employed. Using the optimised conditions, the silver nanoparticles remained stable for periods in excess of 2 months. The nanoparticles were immobilised inside a polyacrylamide hydrogel and used for the reduction of 4-nitrophenol. The rate constant obtained for the reduction of 4-nitrophenol was calculated as 7.1 × 10−4 to 1.6 × 10−3 s−1 depending on the amount of silver. The hydrogel–Ag composite was stable and could be stored for several months, while there was little change in the rate constant when it was repeatedly used.