Importance of Phase Purity in Two-Dimensional β-Co(OH)₂ for Driving Oxygen Evolution

The design and development of efficient electrocatalysts for water splitting, particularly for thermodynamically unfavorable oxygen evolution reaction (OER), is one of the foremost requirements to develop sustainable hydrogen production technologies. This requires a thorough understanding of various characteristics of an electrocatalyst that can influence its performance. Layered hydroxides, such as β-Co(OH)2, are promising OER electrocatalysts; however, they tend to transform to the CoOOH phase during synthesis. In this work, we have evaluated the influence of the oxyhydroxide impurity phase on the OER activity of two-dimensional β-Co(OH)2. Our study reveals that the CoOOH impurity in β-Co(OH)2 nanosheets improves the thermodynamics of OER (overpotentials of 322 and 369 mV at a 10 mA·cm–2 current density in the presence and absence of impurity), while adversely impacting the reaction kinetics (Tafel slopes of 142.3 and 96.5 mV·dec–1, respectively). These concurrent synergistic and antagonistic behaviors of the CoOOH phase are interesting and emphasize the importance of well-controlled synthesis conditions and thorough catalyst characterization to develop sustainable catalytic technologies.