Nano-to-microscale nickel-based electrode architectures for improving the efficiency and performance of electrocatalytic water splitting

Gas-evolving electrodes are hindered by the behavior of "sticky" bubbles that collect on their surfaces. At high overpotentials, a frothy layer of surface adhered bubbles results in a reduced performance and increased resistances by blocking access to the electrolyte. The driving mechanisms behind gas bubble dynamics are challenging scientific questions to address. An improved understanding of the underlying processes could assist in the development of more efficient gas-evolving surfaces. Intentionally designed electrode architectures are sought to direct gas bubble dynamics for an improved efficiency of electrocatalytic water splitting. Recent literature has pointed toward electrode morphologies that can effectively release bubbles without the need for additional energy input (e.g., avoiding the need for high shear flows, ultrasonic frequencies, or external magnetic and gravitational fields). These lessons can be applied to a variety of gas-evolving reactions but are of particular interest for the oxygen evolution reaction (OER). Nickel-based electrodes with unique nano-to-microscale features were prepared to investigate the structure-to-function relationship for improved performance of the OER. The motivation to study earth-abundant nickel (Ni) was driven by its conventional use in alkaline electrolysis systems. Prolonged, oxidative aging of the material was conducted to assess the underlying stability, resulting activity, and for a more accurate evaluation of the activated surfaces. Regular, well-defined features of Ni were fabricated using photolithography and template-assisted methods, while irregular textures with high surface areas were also prepared using high-throughput, scalable techniques. Correlation of the texture to the electrochemical performance of the OER was conducted in the context of gas-evolution dynamics and with consideration to the complex phase transformations of Ni species on the surfaces of these electrocatalysts. The following studies emphasize the importance of sufficiently activating earth-abundant electrocatalytic materials, as well as the importance of assessing the stability of these materials as a result of Ni-Fe (oxy)hydroxide (NiFeOxHy) phase transformations. The results from these studies also suggest that the presence of microscale features with specific dimensions can assist in an efficient removal of gas bubbles during the OER.