Efforts to improve C₂₊ selectivity in CO₂ electroreduction have increasingly focused on strategies that deliberately induce catalyst surface reconstruction to create and maintain active sites. Among these, approaches using anodic pulses have gained particular attention for their ability to modulate the copper catalyst surface in situ. However, the underlying Cu surface reconstruction mechanisms triggered by anodic polarization still remain unclear. Here, we show that applying anodic potentials to copper can lead to two distinct surface reconstructions: surface oxide formation or metal dissolution, each defining a different reconstruction pathway with contrasting impacts on product selectivity. Oxide-derived reconstruction transiently enhances C₂ over C₁ selectivity but gradually loses effectiveness during operation, while dissolution-redeposition reconstruction continuously forms C₂-selective sites, resulting in a progressive increase in C₂ selectivity over time. Leveraging this mechanistic understanding, we implement electrolyte engineering by introducing trace Cu²⁺ ions under cathodic conditions to directly activate the dissolution-redeposition pathway without anodic bias. This strategy drives a dynamic electrochemical interface that sustains active-site regeneration and enables controllable selectivity, offering an energy-efficient alternative.