Modulating metal oxides

The more difficult step in fuel cells and water electrolysis is the oxygen evolution reaction. The search for earth-abundant materials to replace noble metals for this reaction often turns to oxides of three-dimensional metals such as iron. Zhang et al. show that the applied voltages needed to drive this reaction are reduced for iron-cobalt oxides by the addition of tungsten. The addition of tungsten favorably modulates the electronic structure of the oxyhydroxide. A key development is to keep the metals well mixed and avoid the formation of separate phases.

Abstract

Earth-abundant first-row (3d) transition metal–based catalysts have been developed for the oxygen-evolution reaction (OER); however, they operate at overpotentials substantially above thermodynamic requirements. Density functional theory suggested that non-3d high-valency metals such as tungsten can modulate 3d metal oxides, providing near-optimal adsorption energies for OER intermediates. We developed a room-temperature synthesis to produce gelled oxyhydroxides materials with an atomically homogeneous metal distribution. These gelled FeCoW oxyhydroxides exhibit the lowest overpotential (191 millivolts) reported at 10 milliamperes per square centimeter in alkaline electrolyte. The catalyst shows no evidence of degradation after more than 500 hours of operation. X-ray absorption and computational studies reveal a synergistic interplay between tungsten, iron, and cobalt in producing a favorable local coordination environment and electronic structure that enhance the energetics for OER.

Science 15 Apr 2016:
Vol. 352, Issue 6283, pp. 333-337
DOI: 10.1126/science.aaf1525

http://science.sciencemag.org/content/352/6283/333

在电解水的过程中，最困难的一个步骤在于驱动析氧反应的发生。在寻找可以代替贵金属的廉价催化材料时，科学家们最常倾向于三维金属氧化物材料（如铁氧化物）。Zhang等人发现，通过加入金属钨，铁-钴氧化物催化析氧反应的驱动电压可以被有效降低。钨元素可以有效的调节氢氧化物的电子结构，而钨发挥作用的一个关键因素是要使各种金属混合均匀，避免相分离情况的出现。（新材料在线）