The electrocatalytic activities and stabilities of spinel cobalt oxides with different morphologies have been investigated for the oxygen evolution reaction (OER) in an alkaline environment. Spinel cobalt oxide nanoparticles with well-defined cubic and octahedral morphologies were prepared, which predominantly expose the (100) and (111) surfaces, respectively. The OER activity of spinel cobalt oxide, measured in terms of current density, increases with higher relative proportion of the (111) surface, which can be attributed to the higher density of cobalt ions on the (111) surface compared to that on the (100) surface. The surfaces of cobalt oxide nanocubes are slighted reduced compared to those of nanooctahedra prior to OER testing. Based on chronoamperometry experiments, the nanocubes exhibited higher stability compared to the nanooctahedra, which could be due to the lower surface energy of the (100) surface compared to the (111) surface. The dependence of OER activity and stability on spinel cobalt oxide crystal facets demonstrates the importance of surface orientation in catalyst performance optimization.

Electrochemical tip-enhanced Raman spectroscopy (EC-TERS) has been implemented to investigate the structure and activity of iron(II) phthalocyanine (FePc)a model catalyst for the oxygen reduction reaction (ORR). Using EC-TERS, both reversible change and irreversible degradation to FePc have been observed during ORR. The reversible change in the Raman spectrum of FePc can be related to the FePc molecules that adapt a nonplanar geometry during catalysis. In contrast, the irreversible degradation of FePc is a consequence of FePc demetalation, leading to the subsequent formation of free base phthalocyanine. This observation affirms that FePc demetalation during ORR proceeds via a direct loss of Fe 2+ and that carbon corrosion is not the operative mechanism. Importantly, the FePc demetalation process can be correlated with a loss of ORR activity suggesting that Fe-containing sites are essential for FePc to achieve high catalytic activity. This study establishes EC-TERS as a promising technique for the operando characterization of electrocatalytic reactions at the molecular scale.

Synthesis and implementation of highly active, stable, and affordable electrocatalysts for the oxygen evolution reaction (OER) is a major challenge in developing energy efficient and economically viable energy conversion devices such as electrolyzers, rechargeable metal-air batteries, and regenerative fuel cells. The current benchmark electrocatalyst for OER is based on iridium oxide (IrO x ) due to its superior performance and excellent stability. However, large scale applications using IrO x are impractical due to its low abundance and high cost. Herein, we report a highly active hafnium-modified iridium oxide (IrHf x O y ) electrocatalyst for OER. The IrHf x O y electrocatalyst demonstrated ten times higher activity in alkaline conditions (pH = 11) and four times higher activity in acid conditions (pH = 1) than a IrO x electrocatalyst. The highest intrinsic mass activity of the IrHf x O y catalyst in acid conditions was calculated as 6950 A gIrOx –1 at an overpotential (η) of 0.3 V. Combined studies utilizing operando surface enhanced Raman spectroscopy (SERS) and DFT calculations revealed that the active sites for OER are the Ir–O species for both IrO x and IrHf x O y catalysts. The presence of Hf sites leads to more negative charge states on nearby O sites, shortening of the bond lengths of Ir–O, and lowers free energies for OER intermediates that accelerate the OER process.