Thermodynamic Control of Interface Directs MnO₂ Nucleation Chemistry for Dense and Conformal Electrodeposition

Manganese dioxide (MnO₂) is widely recognized as a promising material for high-energy-density energy storage systems due to its broad applicability and facile electrodeposition. However, achieving uniform, thin, and high-mass-loading MnO₂ coatings on high-surface-area electrodes remains a significant challenge. Conventional electrodeposition methods typically yield nonuniform, thick layers with poor conductivity and limited material utilization, restricting their practical use. Here, we uncover a thermodynamically engineered vanadyl/pervanadyl (VO²⁺/VO₂⁺) interface that fundamentally reshapes MnO₂ electrodeposition chemistry, enabling highly uniform and dense coatings. Combining in situ AFM measurement, Classical Nucleation Theory, and Johnson-Mehl-Avrami-Kolmogorov modeling, we show that this interface reduces early-stage detectable MnO₂ island size by 35-fold and shifts the MnO₂ growth from diffusion-limited to reaction-limited progressive nucleation. This thermodynamically controlled interface yields highly dense and conformal MnO₂ films with record-high mass loading of 241 mg cm^-2 (1607 mg cm^-3) on 3D-printed graphene aerogels, without compromising porosity or inducing thickness gradient. As a prototype demonstration, the resulting MnO₂ electrodes deliver record-setting volumetric performance in both capacitors (106 F cm^-3) and Zn//MnO₂ pouch cells (162 mAh cm^-3). Beyond energy storage, our findings demonstrate the significance of thermodynamic interface control in MnO₂ nucleation chemistry for achieving dense and uniform coatings on various substrates, with implications for electrocatalysis, semiconductor processing, and advanced materials manufacturing.