Overcoming Hurdles in Oxygen Evolution Catalyst Discovery via Codesign

Abstract

The oxygen evolution reaction (OER) is central to several sustainable energy technologies. Catalyst development has largely focused on lowering the overpotential and eliminating reliance on precious metals, revealing stark differences in alkaline and acidic OER. In alkaline electrolyte, precious metal-free catalysts have approached the limiting overpotential from established free energy scaling relationships, and our survey of complex metal oxides shows that this limit can be approached with a broad range of catalysts. In acidic electrolyte, electrochemical instabilities create a dual challenge of a dearth of nonprecious metal OER catalysts with overpotential below 0.5 V and a high dissolved metals concentration for most precious metal-free catalysts. On device-relevant time scales, the high dissolved metals concentrations compromise device stability, for example, through a decrease of performance and due to metal exchange between anode and cathode catalysts due to finite permeability of ion exchange membranes. These considerations motivate a substantial increase in monitoring and reporting of dissolved metals concentrations in OER experiments. To facilitate durability-based screening in continued catalyst discovery campaigns, we introduce a durability descriptor based on the d-electron count of each metal element compared to that of its Pourbaix-stable oxidation state, which enables rapid down-selection of candidate metal oxide catalysts. We discuss the importance of a codesign approach to catalyst development, where a device architecture can set specific requirements for dissolved metals concentrations and/or cathode and anode catalysts can be designed to tolerate cross-contamination. This device-level guidance of basic science will facilitate deployment of new catalysts to meet the societal needs for accelerated sustainable technology development.

Zinc Titanium Nitride Semiconductor toward Durable Photoelectrochemical Applications

“…Co-design ensures that integration and scale-up process accompanies each discovered photocatalyst, a transformational research approach that can amplify the impact of discovery science. 14 While the most-investigated photovoltaic materials (Si, III-Vs, and II-VI compounds) have promising properties for PEC applications, all corrode rapidly under electrochemical operation, a result of their low Pourbaix stability. 7,[15][16][17] Substantial efforts have been dedicated to limiting such corrosion, 18,19 but these have failed to generate photoelectrodes with surfaces which are durable for more than tens of hours of operation.…”

“…A key attribute of co-design is disruption of the sequential design process, which for photocatalysts has traditionally been materials discovery based on performance criteria followed by synthesis for device implementation. Co-design ensures that integration and scale-up processes accompany each discovered photocatalyst, a transformational research approach that can amplify the impact of discovery science …”

Stability Design Principles of Manganese-Based Oxides in Acid

“…Notably, although first-row late transition metal oxides based on Fe, Co, and/or Ni have been widely reported with comparable or higher catalytic activity for the alkaline OER and ORR than their precious-metal-based counterparts, these transition metal oxide catalysts are not stable in acid . Mn-based oxides are more stable in acid than those based on late transition metals and can possibly be stabilized by reaching dissolution–deposition equilibrium at moderately acidic pHs, but they still corrode and deactivate in strong acid and after long operation. , To tackle this challenge, extensive efforts over the past decades have been focused on combining active, yet unstable metal oxides (e.g., Mn oxides) with corrosion-resistant oxides (e.g., TiO x , SbO x , − TaO x , WO x , , and PbO x ) − to stabilize those active metal sites in acid. For example, incorporating 20 at.…”

“…% Sb 5+ cations into Mn 2 O 3 has been reported to result in reduced OER currents and lowered metal dissolution rates in 1 M H 2 SO 4 . Interestingly, compared with these two oxides, having a higher fraction of corrosion-resistant elements (e.g., Sb) than Mn cations has given rise to more acid-stable, yet less catalytically active oxides (e.g., MnSb 1.7 O x and MnSb 2 O 6 ), indicating a fundamental activity–stability trade-off …”

“…16 Interestingly, compared with these two oxides, having a higher fraction of corrosion-resistant elements (e.g., Sb) than Mn cations has given rise to more acid-stable, yet less catalytically active oxides (e.g., MnSb 1.7 O x 15 and MnSb 2 O 6 ), 20 indicating a fundamental activity−stability trade-off. 9 To develop Mn-based oxides with an optimal trade-off or bypass this limitation, it is critical to establish oxide stability descriptors in acid. These descriptors offer a fundamental understanding of oxide dissolution and provide new guiding principles to enhance their intrinsic stability.…”