Rechargeable-hybrid-seawater fuel cell

A novel energy conversion and storage system using seawater as a cathode is proposed herein. This system is an intermediate between a battery and a fuel cell, and is accordingly referred to as a hybrid fuel cell. The circulating seawater in this open-cathode system results in a continuous supply of sodium ions, which gives this system superior cycling stability that allows the application of various alternative anodes to sodium metal by compensating for irreversible charge losses. Indeed, hard carbon and Sn-C nanocomposite electrodes were successfully applied as anode materials in this hybrid-seawater fuel cell, yielding highly stable cycling performance and reversible capacities exceeding 110 mAh g−1 and 300 mAh g−1, respectively. A hybrid fuel cell that uses seawater as an active electrode offers a low-cost route to large-scale energy storage, according to a new study. An international team led by Youngsik Kim from Ulsan National Institute of Science and Technology in Korea investigated whether sodium ions could replace increasingly rare lithium ions in an alternative type of battery technology. To achieve this, the researchers designed an ‘open cathode’ layout that continuously circulates seawater — a safe and inexpensive sodium ion source — over anodes made from high-capacity hard carbon or tin-carbon nanocomposites. By providing a near-limitless supply of sodium ions, this concept overcomes the irreversible initial alloying behavior seen in these anodes, thereby providing superior battery recharging capabilities — no change in storage capacity was detectable after 30 charge–discharge cycles. We presented the novel concept of a hybrid-seawater fuel cell, comprising a closed-negative electrode, a NASICON solid electrolyte, and an open-seawater positive electrode. Hard carbon and a Sn-C nanocomposite were successfully applied as alternative anode materials for this hybrid-seawater fuel cell, presenting a highly stable cycling performance and reversible capacities exceeding 110 mAh g−1 and 300 mAh g−1 for hard carbon and Sn-C, respectively. Particularly, in the case of the Sn-C anode, the performance was substantially enhanced by the almost infinite supply of sodium ions using the open system seawater-based positive electrode. Thus, in addition to the simplicity of the overall concept, the utilization of redox processes in seawater represents a new and very promising approach for cost efficient and environmental friendly large-scale energy storage devices.