Thin layers formed by the arrays of the vertically oriented 2-dimensional nanocrystals of Birnessite-type manganese oxide Cu _x MnO ₂ ∙nH ₂ O were synthesized for the first time by the reaction of gaseous ozone with the surface of aqueous solutions of manganese (II) acetate and copper (II) acetate salts mixture. The obtained layers were placed onto the surface of indium tin oxide (ITO)–coated glass electrodes and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-Ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The electrochemical performance of the layers was examined by cyclic voltammetry (CV). It was found that the synthesized structures are formed by the 2D nanocrystals with the thickness of 3–6 nm. The atomic concentration of copper x depends on the ratio of Cu(CH ₃ COO) ₂ and Mn(CH ₃ COO) ₂ solution concentrations and can be as much as 0.35. The obtained layers were tested as the electrochemical platform for nonenzymatic hydrogen peroxide sensing. It was shown that the electrode can provide an ultrasensitive H ₂ O ₂ determination with the limit of detection of 0.4 nМ and linear concentration range that lies in the region of nanomolar concentrations. We assume that the observed effects are due to the morphology of the synthesized layers, which ensures maximum contact of the analyte with the active sites of 2D nanocrystals of Cu _x MnO ₂ ∙ nH ₂ O. Comparison of the obtained analytical characteristics with the literature data indicates the good prospects of the synthesized nanomaterial for its use as a working electrode for nonenzymatic H ₂ O ₂ sensor.