Nanoscale limitations in metal oxide electrocatalysts for oxygen evolution

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Metal oxides are earth-abundant and low-cost materials with potential as electrocatalysts.
• Their inherent insulating nature hinders widespread application in electrocatalysis.
• Nanostructuring offers a pathway to utilize these materials by facilitating charge transport via quantum tunneling.

Purpose of the Study:

• To determine the critical thickness of insulating metal oxide films required for efficient charge transport via tunneling.
• To establish a theoretical framework for predicting this critical thickness in nanostructured electrocatalysts.
• To provide guidelines for designing optimal nanoparticle oxide electrocatalysts.

Main Methods:

• Theoretical analysis to determine the critical thickness for electron tunneling at a specific current density.
• Electrochemical measurements on conformal thin films synthesized using atomic layer deposition (ALD).
• Validation of theoretical predictions with experimental data using titanium dioxide (TiO2) as a model system.

Main Results:

• A critical thickness of approximately 4 nm was identified for TiO2, enabling tunneling at a current density of ~1 mA/cm(2).
• Experimental results using ALD-grown TiO2 films corroborated the theoretically derived critical thickness.
• A generalized theoretical relationship was established between critical thickness and the valence band maximum relative to the electrochemical potential.

Conclusions:

• Nanostructuring, specifically achieving a critical thickness of ~4 nm, is crucial for overcoming the insulating nature of metal oxides in electrocatalysis.
• The derived theoretical relationship provides a fundamental understanding for designing efficient nanostructured metal oxide electrocatalysts.
• This work offers essential nanostructuring requirements for the development of cost-effective and earth-abundant electrocatalysts.