that B-or N-centered HTs based 2D polymers are single-band semiconductors with high carrier mobility for either exclusively electrons (B center) or holes (N center), and the appropriate band edge alignment render them potential photocatalysts for either HER or OER processes, respectively, and coupling them in a tandem cell with spatially separate electrodes allows water splitting without the emergence of explosive H2/O2 mixture, yet at the expense of a 2-photon process per excited charge carrier.