Direct Electrosynthesis of C ₃₊ Hydrocarbons from CO ₂ via Size-Controlled Nickel Nanoislands on a Carbon Support

Direct synthesis of C 3+ hydrocarbons via the electrochemical CO 2 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 C 3+ 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 C 2 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 C 3+ hydrocarbon formation. Nanoislands as small as ∼3.5 nm delivered a 120-fold increase in C 3+ hydrocarbon specific activity relative to large particles (bulk-like Ni). CO stripping voltammetry shows weaker *CO adsorption on isolated nanoislands. While C 3+ 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 CO 2 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.