Layered double hydroxides for sustainable hydrogen production from seawater

This work presents investigations on the Oxygen Evolution Reaction (OER) under Alkaline Seawater conditions, using a range of microporous/mesoporous oxide/hydroxide catalysts, notably, Layered Double Hydroxides (LDHs). This study explored a one-step method of coating LDHs onto Ni foams by Hydrothermal Synthesis (directly onto a Ni foam), Dip-coating of Fe, Ni solutions onto the Ni foam and Electrodeposition of LDH onto the Ni foam as well. Hydrothermal Synthesis with direct deposition was considerably stable compared to the other methods, and this research was able to report the electrochemical OER performance on a range of compositions, viz. Ni–Fe in several ratios, and also ternary systems like Ni–Co–Fe. The electrochemical measurements (CV and LSV) showed that Ni–Fe LDHs with Ni: Fe in a 4:1 ratio gave the lowest overpotential (330 mV at 100 mA/cm²) in sea water, which was very much in sync with reported literature on conventional fresh alkaline water – the role played by doping of Ni by Fe, and others like Co, and their oxidation states (examined by XPS) holds the key to enhancing the OER catalytic activity, which is critical for operability in seawater, thus contributing to sustainable and environmentally friendly hydrogen production. This study also demonstrates that Chlorine/Hypochlorite chemistry is largely suppressed under these highly alkaline conditions as predicted by the Pourbaix diagram, although a more extensive degradation study for all cell components is ongoing.