Recently, Nocera and co-workers reported the activity and stability of a novel MnOx based OER
catalyst, from pH 1 to 13.35 They demonstrated that at pH as low as 1, MnO2 can catalyze oxygen
evolution within the range of its bulk thermodynamic stability, as shown in Figure 1. However, in
order to utilize MnO2 in PEM electrolyzers, it will be essential to stabilize the surface at potentials
positive of the standard dissolution potential, 1.7 VRHE.28
Consequently, a key challenge, which has not been addressed thus far, is the development of active
and stable catalysts for the OER in acid, which are free of precious metals. Herein, we develop a
strategy to address this challenge. We employ density functional theory (DFT) calculations to
investigate the feasibility of meta-stabilizing an oxide OER catalyst. Based on our calculations, we
synthesize the oxides in the form of sputtered thin films. We test their catalytic activity and stability
using our recently developed method,32 combining electrochemical techniques, quartz crystal
microbalance (QCM) and inductively coupled plasma mass spectrometry (ICP-MS).
2. Results and Discussion
2.1 Theoretical calculations
The anodic dissolution of MnO2 in acid proceeds through the formation of the higher oxide MnO4
- as
described in Equation (1):
− + 4H+ + 3e− Equation (1)
MnO2 + 2H2O → MnO4
The dissolution will proceed via the surface, where a variety of different sites will be present. The sites
that dissolve at the lowest overpotential can be identified by invoking a simple argument, based on
the cost in terms of surface energy. Terrace atoms are less prone to dissolution, as their removal
would leave behind vacancies, which inherently have a high surface energy. On the other hand,
removal of a stepped row or a kink site leads to the same surface structure; hence, no cost in surface
energy is associated with the process. Therefore, the dissolution of under-coordinated sites is favored
over the dissolution of terrace sites. DFT models describing the dissolution of metal surfaces yielded
similar results.49,50 According to our present understanding, the coordinatively unsaturated (CUS)