Material Changes in Electrocatalysis: An In Situ/Operando Focus on the Dynamics of Cobalt‐Based Oxygen Reduction and Evolution Catalysts

Abstract

The shift towards cheaper, non‐platinum group metal electrocatalyst materials for clean energy technologies is coupled with challenges in maintaining long‐term performance. For practical purposes, electrocatalytic stability typically focuses on catalyst electrochemical performance over time. However, a deeper understanding of catalyst material property changes during operation is needed to enable material‐specific design strategies for long‐term stabilization. In the last several decades, improvements in material characterization techniques have made it possible to probe the composition, structure, and degradation products of catalysts in situ/operando. Herein we review the current understanding of in situ/operando material stability of Co‐based electrocatalysts for the oxygen evolution (OER) and reduction reactions (ORR) in acidic and alkaline environments. We focus on in situ/operando materials characterization of three categories of Co‐based OER/ORR catalysts: oxides and (oxy)hydroxides, mixed‐metal catalysts, and non‐oxide materials. This review aims to compile and compare the results from multiple studies and techniques to provide insight into the role that the starting material, pH, and applied potential have on the active surface and stability of Co‐based materials. We conclude by highlighting directions that have been underexplored with opportunities for continued research including improving in situ/operando characterization, methods to probe long‐term material changes, and the development of operando studies on full‐scale devices. Using Co‐based materials as a case study, this review shows the vital role that in situ/operando characterization must play in the future of improving electrocatalyst stability.

Electrically Insulated Catalyst–Ionomer Anode Interfaces toward Durable Alkaline Membrane Electrolyzers

“…Ir-based OER catalysts are known to slowly leach during operation, and dissolution rates are faster for oxidized metallic Ir compared to crystalline rutile IrO 2 . − It is possible that the added HfO x layers may protect and stabilize the surface of the Ir catalyst layer from dissolution, leading to lower cell voltages in durability test data. The CoO x model catalyst we prepared here appears stable in its oxide form and may have less dissolution under OER conditions intrinsically, thus being less affected by the presence of the HfO x coatings. While the scope of this study is the role of passivation coatings in ionomer degradation, further study focused on catalyst degradation/dissolution using online inductively coupled plasma mass spectrometry (ICP-MS) , would be helpful to determine the role of HfO x , or other, coatings in stabilizing catalyst layer specifically.…”

“…54−56 It is possible that the added HfO x layers may protect and stabilize the surface of the Ir catalyst layer from dissolution, leading to lower cell voltages in durability test data. The CoO x model catalyst we prepared here appears stable in its oxide form and may have less dissolution under OER conditions intrinsically, 57 degradation, further study focused on catalyst degradation/ dissolution using online inductively coupled plasma mass spectrometry (ICP-MS) 58,59 would be helpful to determine the role of HfO x , or other, coatings in stabilizing catalyst layer specifically. In summary, a new passivated anode for AEMWE has been developed where the OER catalysts are directly deposited on the GDLs, and the surface of the catalysts is protected with thin films of ion-permeable but electron-blocking metal oxide films, here ALD HfO x .…”

Silver-integrated cobalt hydroxide hybrid nanostructured materials for improved electrocatalytic oxygen evolution reaction

“…[38][39][40] Furthermore, MO 6 structure of Co(OH) 2 is considered to be conducive for OER. 41 However, the poor electronic conductivity and low natural activity, along with the poor adsorption of OH À due to the Co 2+ oxidation state, limit their application potential. [42][43][44][45][46] Amorphous cobalt hydroxides were also explored for improving the active sites due to their structural defects and short-range bonding order.…”

Regulating Excess Electrons in Reducible Metal Oxides for Enhanced Oxygen Evolution Reaction Activity: A Mini‐Review

“…[8] Therefore, substantial research efforts have been dedicated to unraveling the OER mechanism and developing strategies for designing highly efficient OER catalysts. [3,[9][10][11][12][13][14][15] Since the early 20th century, the Sabatier principle has been empirically discovered to elucidate catalytic activity, [20] providing a guiding framework for the rational design of catalysts. [19,21] This principle establishes a link between the micro-level adsorption properties of reaction intermediates and the macrolevel catalytic activities.…”

“…However, the scarcity, high cost, and susceptibility to dissolution impede their large‐scale commercial utilization [8] . Therefore, substantial research efforts have been dedicated to unraveling the OER mechanism and developing strategies for designing highly efficient OER catalysts [3,9–15] …”