CBE Colloquia - Combining PLASMA and the SEA: Synthesis of high-performance chlorine-resistance catalysts for seawater-based electrochemical devices

Seawater-based electrochemical devices are promising large-scale energy storage devices and are highly compatible with offshore ocean locations or large-scale maritime applications. However, the components of seawater, in particular, chlorine anions (Cl–), block the metal surface and hinder the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In particular, platinum or metal-based electrocatalysts often suffer a severe reduction in catalytic activity due to the strong adsorption of Cl– on the catalyst surface. As a result, the ORR/OER electrocatalyst/active sites must be prevented from adsorbing Cl– during reactions. Our group has utilized a carefully engineered interface that uses the dipole moments of metal-core/graphene-layer heterojunctions to block the Cl– by Coulomb repulsion. Density functional theory (DFT) calculations demonstrated that Cl– ions can be repelled by the strong negative electric fields induced near the catalytic active sites on the surfaces of the catalysts. Experimentally, we applied a novel synthesis method, plasma engineering, to fabricate the various metal/N-doped graphene electrocatalysts.

We have, for example, designed a cathode for rechargeable seawater batteries (SWBs) with cobalt-core/pyridinic-N-doped graphene (Co-N/C) as a highly active, Cl-resistant bi-functional electrocatalyst. The cathode catalysts in a practical seawater demonstrate a voltage gap of 0.56 V, which is superior to 20 wt.% Pt/C (0.73 V) at the initial discharge–charge cycle. Furthermore, the extremely high stability of Co-N/C catalysts, thanks to the protection layer of N-doped carbon and its chlorine-repulsion effect, was demonstrated in a 100-hour charge–discharge cycling test. A similar concept has been applied to fabricate a hybrid electrocatalyst composed of FeCoS embedded in a polyaniline matrix (FCS-PANI) as a Cl-resistant anode catalyst in seawater electrolysis. Outstanding OER performance with a low overpotential of 327 mV at 50 mA cm−2 was achieved by electrochemical testing in alkaline seawater. In particular, when integrated into an anion exchange membrane water electrolyzer (AEMWE), it shows ultra-high stability and low degradation (0.3 mV h−1) over 500 h, and 99.97% hydrogen purity was obtained, indicating its practical potential for large-scale seawater electrolysis. 

In summary, this presentation provides new insights into the application of plasma engineering to the design of high-performance, durable electrocatalysts for a wide range of seawater-based energy devices.