CuMnO2 is prepared via Cu+ -> Li+ exchange in molten copper (I) chloride. It crystallizes in a monoclinic structure (SG C2/m) where the MnO6 octahedra elongation is ascribed to the Yahn-Teller (Y-T) effect of Mn3+ ions. From chemical analysis, the oxide is more accurately formulated as CuMnO2.01. Above 250 degrees C, it undergoes a reversible transition to spinel Cu (x) Mn3-x O-4 and beyond 940 degrees C it converts back to Cu1.1Mn0.9O2. Extrapolation of high-temperature magnetic data indicates T-intercept theta(p) of -450 K and an effective moment of 5.22 mu(B), consistent with strong antiferromagnetism in the basal plans and high spin (HS) configuration Mn3+. This value is slightly larger than that of the spin only moment, a behavior ascribed to Cu2+ originating from oxygen insertion. As prepared, CuMnO2 displays p-type conductivity with an activation energy of 0.16 eV. Most holes generated upon band gap excitation are trapped on Cu+ ions and the conduction occurs by small polarons hopping between neighboring sites. The linear increase of thermopower for Cu1.05Mn0.95O2 with temperature indicates a hole mobility mu(300 K) (3.5 x 10(-6) cm(2) V-1 s(-1)) thermally activated. CuMnO2 is made p- and n-type and the difference in the carriers mobilities is attributed to different oxygen polyhedra. The title oxide, characterized photo electrochemically, exhibits a pH-insensitive flat band potential (+0.13 V-SCE). The valence band, located at 5.3 eV below vacuum, is made up of Cu 3d orbital. As application, the powder showed a good performance for the H-2-photo evolution.