Techniques are disclosed for electrochemical synthesis of rechargeable battery cathode precursor materials using a porous carbon element. The porous carbon element acts as an air cathode to reduce oxygen. Reduced oxygen species may oxidize a transition metal anode, thereby facilitating a room temperature redox reaction with transition metals, including those that are generally resistant to corrosion, such as nickel. The transition metal reaction product(s) may be further processed into rechargeable battery cathode materials without also synthesizing hazardous waste products.