The dissolution behavior of La2Cu4 has been examined by electrochemical techniques in aqueous media under open-circuit conditions at 298 K. La2CuO4 is dissolved by aqueous acid at proton-mass transport limited rates in 1 M NaCl. Rotating ring-disk electrode (RRDE) techniques were employed in collection (product detection) and shielding (reactant removal) measure modes to monitor the surface chemistry, including a new approach not involving separate disk electrode H+ reduction measurements as required heretofore.(6) Related techniques monitoring the competitive oxygen evolution reaction were used to study the coulometric efficiency of anodic formation of the superconductor phases, La2CuO4+x, in alkaline medium. Solid-state diffusion severely limits growth.