The Technology
Electrode quality for electrochemical conversion needs material improvement and design. For instance, conversion efficiencies of photoelectrochemical cells used for water splitting reaction are limited by the intrinsic material properties of the electrode. The electrode should be a good conductor, a good solar light absorber, a good catalyst, and have an appropriate band edge alignment for water splitting. Furthermore, the electrode should be relatively inexpensive, abundant, nontoxic, and maintain stability in operating conditions.
Most materials do not have all these properties simultaneously. For example, some dopants that increase electronic conductivity and light absorbance of the hematite-based electrodes may have a negative effect on the chemical reactivity of the electrode. It has been found that platinum, while enhancing the electron conductivity of Fe2O3 in the bulk of the electrode, increases the overpotential for water oxidation, when present near the surface of the electrode.
There are several techniques to improve electrical conductivity and reactivity such as doping, but they change the material homogenously and tend not to improve all properties.
However, gradient doping (with one or more dopants) causes material composition in the bulk to be different than the material composition at its surface. For example, in the bulk, the material will include a higher concentration of dopants that enhance electron conductivity. At the surface, the material will have a lower concentration of these dopants since they inhibit chemical activity, but other dopants that can improve catalytic properties could be used in higher concentration close to the surface.
Advantages
- Higher efficiency
- Lower over potential
Applications and Opportunities
- Photo-electrodes for water splitting and other reactions
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