In an effort to transition from petroleum-based fuels, vehicles such as the Hyundai Tucson Fuel Cell are becoming more widespread. However, the inherent safety and cost of compressed hydrogen tanks are still in question. Electrolytic water splitting represents the most environmentally friendly alternative to generate hydrogen gas; however, the kinetics of the oxygen evolution reaction (OER) are slow and require a catalyst. Most catalysts to date have been limited to transition metal oxides or noble metals – both of which are expensive and unsustainable. The report by Lu et al. reports that unexpectedly high OER catalytic activity was achieved by oxidized multi-walled carbon nanotubes (MWCNTs). A variety of precursors may be used to synthesize MWCNTs, which has resulted in lower costs and ready availability of these nanostructures.
In this work detailing the development of metal free electrocatalysts, it was discovered that surface-oxidized MWCNTs, post-treated by hydrothermal and electrochemical activation treatments, showed unprecedented OER activity even in the absence of surface metal oxide catalysts. This OER activity was rationalized by the oxygen containing functional groups such as ketonic C-O, which altered the electronic distribution of the surrounding carbon atoms at the MWCNT surfaces, thereby facilitating the adsorption of water oxidation intermediates. These findings open the door to new applications of surface-oxidized MWCNTs for catalyzing a class of important anodic reactions in water splitting and fuel cells. Further improvements of the activity of the surface-oxidized carbon nanomaterials may enable the fine-tuning of the structure and compositions of hybrid carbon materials for specific applications. These findings provide a prime example of sustainable pathways for nanotechnology to solve critical environmental and societal issues.
Reference: Lu X, Yim W-L, Suryanto BHR, Zhao C. Electrocatalytic Oxygen Evolution at Surface-Oxidized Multiwall Carbon Nanotubes. J. Am. Chem. Soc. 2015; 137 (8): 2901-2907 doi: 10.1021/ja509879r
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