Direct Electrosynthesis of C₃₊ Hydrocarbons from CO₂ via Size-Controlled Nickel Nanoislands on a Carbon Support

Direct synthesis of C₃₊ hydrocarbons via the electrochemical CO₂ reduction reaction is highly desirable for producing sustainable chemicals. However, this approach remains challenging due to the limited ability of current electrocatalysts to adsorb and couple key reaction intermediates effectively, with promising systems, such as Ni oxyhydroxide-derived catalysts, still exhibiting partial current densities toward C₃₊ hydrocarbons <0.9 mA cm^-2. Motivated by the limited activity and control over the active site environment of these systems, we hypothesize that reducing the size of metallic Ni modifies its electronic states and introduces interfacial metal-support sites that promote more balanced *CO adsorption, critical for facilitating C-C coupling beyond C₂ intermediates. Here, we report a plasma-assisted deposition method to synthesize size-controlled metallic Ni nanoislands on a carbon support. Characterization revealed that reducing the nanoisland size (<12 nm) forms undercoordinated, electron-deficient, and strained surfaces with a downshifted d-band center─features associated with weakened *CO binding, favoring intermediate coupling and C₃₊ hydrocarbon formation. Nanoislands as small as ∼3.5 nm delivered a 120-fold increase in C₃₊ hydrocarbon specific activity relative to large particles (bulk-like Ni). CO stripping voltammetry shows weaker *CO adsorption on isolated nanoislands. While C₃₊ partial current densities remain low (∼0.1 mA cm^-2), these findings identify nanoparticle size and metal-support interactions as key design parameters for advancing CO₂ conversion to long-chain hydrocarbons, offering a foundation for further improvement, as demonstrated by a >20-fold enhancement in the Ni-mass-based activity versus state-of-the-art catalysts.