MOCVD-Derived Manganese Nitride Films as Rapid Charging, High-Capacity Electrodes Materials for Next Generation Supercapacitors

Abstract

The search for cost-effective and high-performance electrode materials is central to improving the efficiency of electrochemical energy storage devices. While activated carbons and graphene-based composites are widely adopted for electric double-layer capacitors (EDLCs), their relatively low energy density restricts broader application in hybrid supercapacitors. Transition metal nitrides, by contrast, offer high electrical conductivity and pseudocapacitive behavior, positioning them as attractive alternatives. Among these, manganese nitride (MnN) stands out due to its favorable electronic structure, mechanical stability, and environmental safety. This study reports the synthesis, structural evaluation, and electrochemical performance of MnN thin films fabricated via metal–organic chemical vapor deposition (MOCVD), with particular emphasis on cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The MnN films were deposited on stainless steel substrates using a hexamethylenetetramine-based precursor at considerably low temperatures of <523 K. Structural analysis confirmed uniform nanostructures with interconnected porosity, a critical attribute for facilitating electrolyte penetration and rapid ion transport. Morphological observations revealed dense but conformal surfaces, while energy-dispersive X-ray spectroscopy verified stoichiometric Mn–N formation. These characteristics establish a favorable platform for capacitive charge storage. Electrochemical testing was performed in a three-electrode configuration with 1 M KOH electrolyte. EIS measurements produced Nyquist plots that exhibited near-vertical lines in the low-frequency region, demonstrating a dominantly capacitive response. The equivalent series resistance (ESR) was measured at ~10.3 Ω, reflecting both the intrinsic conductivity of the nitride films and effective electrolyte–electrode interactions. The combination of low ESR and porous nanostructure implies reduced ohmic losses and rapid ion diffusion, both essential for high-rate charge–discharge cycling. MnN electrodes displayed quasi-rectangular voltammograms across multiple scan rates, highlighting the coexistence of electric double-layer formation and fast surface redox reactions. The maximum areal capacitance obtained was 16 mF·cm⁻² at 10 mV·s⁻¹, nearly double that of comparable vanadium nitride electrodes. Furthermore, the capacitance retention at higher scan rates confirmed the ability of MnN thin films to sustain rapid charge–discharge processes without significant loss of performance. Such electrochemical stability indicate their potential for real-world applications where both high-power density and extended cycling are required. These findings demonstrate that MOCVD-derived MnN thin films can bridge the performance gap between traditional carbon-based EDLCs and transition metal oxides. By combining double-layer capacitance with pseudocapacitive kinetics, MnN electrodes deliver enhanced energy storage while maintaining rapid charge delivery. Their environmental benignity, scalable synthesis, and compatibility with hybrid supercapacitor architectures make them promising candidates for portable electronics, regenerative braking in vehicles, and integration into renewable energy systems. This work highlights the importance of coupling advanced synthesis techniques with in-depth electrochemical evaluation. As emphasized by previous studies, tailoring electrode structure at the nanoscale remains key to unlocking superior energy storage performance. The results presented here reaffirm that manganese nitride thin films represent a practical pathway toward next-generation, rapid-charging supercapacitors that combine high energy density with long-term stability. Figure 1