Development and performance enhancement of seawater-based hybrid metal-air and carbon dioxide batteries

Abstract

Owing to the demand for low-cost batteries with safety, hybrid metal-air and carbon dioxide batteries have received considerable attention as new energy storage system (ESS). In this dissertation, nanostructured and N and P dual-doped hard carbon was fabricated by simply carbonizing abundant biomass, pine pollen. The oxygen elecrtrocatalytic performance of pine pollen carbon (PPC) for a cathode is confirmed by a seawater half-cell test, which exhibit the lowest overpotential among Pt/C (20 wt%) and commercial hard carbon (HC) electrodes. The sodium-storage performance of PPC is tested using a coin-type Na half-cell, which exhibit a higher reversible capacity than that of the HC electrode. To reduce the manufacturing cost, this battery, comprising both PPC electrodes at the anode and cathode, are fabricated and show an EE of 74%. Next, hybrid Na-CO$_2$ batteries which utilize the high driving force of Na was designed to achieve high energy density and produce C$_2$ chemicals. This system produced CO, formate, and C$_2$ chemicals with 97.0%, 70.4%, and 37.6% FE, generating a high power density (25.0 mW cm$^{-2}$). Furthermore, an anode-less hybrid Na-CO$_2$ battery that harvests unlimited Na ions from seawater instead of difficult-to-handle Na metal anode was constructed, producing CO with an 85.0% FE.