Spatially selective adsorption of 1,3-diethyl-2-thiourea suppresses curvature-accelerated copper nodule growth: In situ SHINERS and multiphysics evidence

DTU suppresses curvature-accelerated copper nodule growth. • In situ SHINERS reveals geometry-dependent DTU adsorption on Cu. • Multiphysics simulation links nodule height to apex thickening. • DTU smooths nodular and planar Cu deposits in acidic electrolyte. Copper nodulation is a critical interfacial instability in copper electrodeposition under electrorefining-relevant acidic CuSO₄/H₂SO₄ conditions, where protrusion curvature intensifies local current density, Cu 2+ flux, and preferential deposition. Here, 1,3-diethyl-2-thiourea (DTU) was evaluated as a thermally durable thiourea analogue for suppressing curvature-accelerated nodule growth on a model copper nodular electrode containing nodular surface (NS) and planar surface (PS) regions. Electrochemical measurements, in situ shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), COMSOL simulations, density functional theory (DFT) calculations, and deposit characterizations were combined to correlate local current focusing, additive-related interfacial responses, and deposit evolution. COMSOL simulations showed that increasing nodule height intensified current focusing, with the maximum local current density reaching 366 A m −2 on the 2 mm nodule. Compared with thiourea (TU), DTU induced stronger cathodic polarization, decreased the anodic stripping response, delayed nucleation transients, increased charge-transfer resistance, and introduced an additional adsorption-related interfacial polarization response. Thermal degradation analysis demonstrated the higher solution-phase durability of DTU, while DFT calculations suggested stronger relative DTU–Cu interactions on representative Cu surfaces. Cu 2+ -free SHINERS revealed potential-dependent and spatially heterogeneous TU/DTU-related interfacial responses, with DTU maintaining clearer molecular signals over a broader cathodic potential range. SEM and AFM confirmed that DTU reduced the average surface roughness from 84.8 ± 6.2 to 22.3 ± 1.7 nm on the NS and from 55.3 ± 4.4 to 9.14 ± 0.8 nm on the PS. Overall, DTU suppresses curvature-accelerated nodule growth by inducing adsorption-mediated kinetic inhibition, thereby weakening the conversion of curvature-enhanced current density into excessive local copper growth.