We have studied a new type of heterogeneous composite electrode featuring a ruthenium(II)-quaterpyridinium complex (Ru3PHOS) bearing six phosphonate groups for strong chemisorption on TiO 2 . Ru3PHOS@TiO 2 has then been deposited on microscopy glass slides using Ag-doped epoxy glue. Nanomolar amounts of palladium have been electrodeposited onto the Ru3PHOS@TiO 2 . To our surprise, we have observed the deposition of carbon needles onto the composite material when (photo)electrochemically reducing bicarbonate from aqueous buffers.