Researchers from the University of Houston have reported a significant breakthrough with a new oxygen evolution reaction catalyst that, combined with a hydrogen evolution reaction catalyst, achieved current densities capable of supporting industrial demands while requiring relatively low voltage to start seawater electrolysis. Researchers say the device, composed of inexpensive non-noble metal nitrides, manages to avoid many of the obstacles that have limited earlier attempts to inexpensively produce hydrogen or safe drinking water from seawater.
a major obstacle has been the lack of a catalyst that can effectively 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 problematic, in part because chlorine requires just slightly higher voltage to free than is needed to free hydrogen.
The catalysts were integrated into a two-electrode alkaline electrolyzer, 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 centimeter (a measure of current density, or mA cm-2) ranged from 1.564 V to 1.581 V.
The voltage is significant, Yu said, because while a voltage of at least 1.23 V is required to produce hydrogen, chlorine is produced at a voltage of 1.73 V, meaning the device had to be able to produce meaningful levels of current density with a voltage between the two levels.
Abstract
Seawater is one of the most abundant natural resources on our planet. Electrolysis of seawater is not only a promising approach to produce clean hydrogen energy, but also of great significance to seawater desalination. The implementation of seawater electrolysis requires robust and efficient electrocatalysts that can sustain seawater splitting without chloride corrosion, especially for the anode. Here we report a three-dimensional core-shell metal-nitride catalyst consisting of NiFeN nanoparticles uniformly decorated on NiMoN nanorods supported on Ni foam, which serves as an eminently active and durable oxygen evolution reaction catalyst for alkaline seawater electrolysis.
Combined with an efficient hydrogen evolution reaction catalyst of NiMoN nanorods, we have achieved the industrially required current densities of 500 and 1000 mA cm−2 at record low voltages of 1.608 and 1.709 V, respectively, for overall alkaline seawater splitting at 60 °C. This discovery significantly advances the development of seawater electrolysis for large-scale hydrogen production.