#seawater

University of Houston Texas Center for Superconductivity Director, Zhifeng Ren. Image credit: University of Houston. 

By Anthony Caggiano

A new catalyst has enabled hydrogen to be made from seawater. 

University of Houston, USA, researchers found combining an oxygen and a hydrogen evolution reaction catalyst together achieved current densities capable of supporting industrial demands while requiring relatively low voltage to start seawater electrolysis.

The researchers said the device, made with non-noble metal nitrides, avoids obstacles that have made it difficult to make hydrogen or safe drinking water from seawater. 

University of Houston Texas Center for Superconductivity Director, Zhifeng Ren, said a major issue had been that there wasn’t a catalyst that could split seawater to produce hydrogen without also setting free ions of sodium, chlorine, calcium and other components of seawater, which once freed can settle on the catalyst and render it inactive. Chlorine ions are especially challenging, in part because chlorine requires only a slightly higher voltage to free than is needed to free hydrogen.

The researchers designed and synthesised a 3D core-shell oxygen evolution reaction catalyst using transition metal-nitride, with nanoparticles made of a nickle-iron-nitride compound and nickle-molybdenum-nitride nanorods on porous nickle foam.

University of Houston Postdoctoral Researcher and first paper author, Luo Yu, said the new oxygen evolution reaction catalyst was paired with a hydrogen one of nickle-molybdenum-nitride nanorods.

The catalysts were integrated into a two-electrode alkaline electrolyser, which can be powered by waste heat via a thermoelectric device or by an AA battery.

Cell voltages required to produce a current density of 100 milliamperes per square centimetre (a measure of current density, or mA cm-2) ranged from 1.564V to 1.581V.

The voltage is significant, Yu said, because while a voltage of at least 1.23V is required to produce hydrogen, chlorine is produced at a voltage of 1.73V, meaning the device had to be able to produce meaningful levels of current density with a voltage between the two levels.

The researchers tested the catalysts with seawater drawn from Galveston Bay, off the Texas coast. Ren said it also would work with wastewater.

The work is described in Nature Communications.