Electroreduction of alkaline/natural seawater: Self-cleaning Pt/carbon cathode and on-site co-synthesis of H2 and Mg hydroxide nanoflakes

Abstract

Distributed coastal/offshore seawater splitting plants can facilitate H₂-based economy’s global deployment. Increasingly, studies emerge mostly focusing on inhibiting anodic oxidation of halide ions. Equally tricky cathodic precipitation in natural seawater reduction (NSR) is neglected due to the use of alkaline seawater in most studies. Herein, we explore possible strategies (introducing a proton sponge to change cathodic microenvironments, breaking local OH⁻ gradients, employing self-cleaning cathodes) to alleviate surface precipitation. We introduce a famous H₂ evolution-active metal, Pt, onto a self-cleaning carbon support with H₂ gas evacuation capability. Our proposed binder-free Pt/carbon cathode is more robust than many previous Pt/C cathodes for NSR. Moreover, we highlight possibilities of co-electrosynthesizing nano-sized Mg hydroxides and H₂ from natural seawater. This work suggests that designs of local environments, pH gradient disruption, and/or cathode architecture-based gas/liquid flows may suppress surface precipitation. We demonstrate in detail the various issues in NSR and possible solutions.