Two-dimensional (2D) transition metal dichalcogenides (TMDCs), due to their unique physical properties, have a wide range of applications in the next generation of electronics, optoelectronics, and valleytronics. Large-scale preparation of high-quality TMDCs films is critical to realize these potential applications. Here we report a study on metal-organic chemical vapor deposition (MOCVD) growth of wafer-scale MoSe₂ films guided by the crystalline step edges of miscut sapphire wafers. We established that the nucleation density and growth rate of MoSe₂ films were positively correlated with the step-edge density and negatively with the growth temperature. At a certain temperature, the MoSe₂ domains on the substrate with high step-edge density grow faster than that with low density. As a result, wafer-scale and continuous MoSe₂ films can be formed in a short duration (30 min). The MoSe₂ films are of high crystalline quality, as confirmed by systematic Raman and photoluminescence (PL) measurements. The results provide an important methodology for the rapid growth of wafer-scale TMDCs, which may promote the application of 2D semiconductors.

The low anodic oxidation potential severely suppresses the output voltage (≤ 0.6 V) of MXene-based symmetrical aqueous micro-supercapacitors (MSA-MSCs) employing acidic electrolytes. Herein, a surface terminals reconstruction mechanism on cathode of MSA-MSCs adopting aqueous neutral electrolyte (1 M Na₂SO₄) is first revealed by systematical electrochemical experiments and in/ex-situ spectral analysis, which indicates that: the -O terminals on Ti₃C₂T_x flakes of cathode can combine with intercalated Na⁺ cations during charging process to reconstruct into -ONa units to (i) inhibit the splitting reaction of adjacent water molecules, decreasing cathodic hydrogen evolution potential, and more significantly, (ii) lower the potential of zero voltage (P_0V) between the symmetrical electrodes to avoid anode oxidation, enabling full use of the unexploited potential range of cathode. Thus, the output voltage of the MSA-MSCs tremendously expanded from 0.6 V in acidic polyacrylamide (PAM)/1 M H₂SO₄ hydrogel electrolyte to 1.5 V in neutral polyacrylamide/1 M Na₂SO₄ hydrogel electrolyte, boosting the corresponding areal energy density from 9.9 to 34.6 μW·h·cm^–2. The demonstrated deep insight on the surface terminals reconstruction mechanism for synchronously modulating the P_0V between symmetrical electrodes and hydrogen evolution potential on cathode provides critical guidance for widening the cell voltage of MSA-MSCs with safer and more inexpensive neutral electrolytes.