A method of operating a flow cell. The method comprises providing a flow cell suitable for generating electrical power from hydrogen and a metal electrolyte. Said flow cell comprises a precipitate of metal oxi and said metal oxide comprises vanadium or manganese. The method further comprises electrochemically generating a redox active precipitate removal species from a precursor species, wherein said redox active precipitate removal species is capable of converting said metal oxide. The method further comprises exposing said metal oxide to said redox active precipitate removal species to effect conversion of the metal oxide.