Due to a limited understanding of how nonprecious materials degrade within sustainable energy technologies, the development of more durable devices is consequently hindered. Specifically, for proton exchange membrane fuel cells and water electrolyzers, metallic cobalt (Co) must often be combined with precious metals or other stabilizers due to its high instability in acidic media. To fundamentally understand the mechanisms behind Co instability, we apply an experimental platform that utilizes on-line inductively coupled plasma mass spectrometry (ICP-MS) to quantify Co dissolution and electrochemical mass spectrometry (EC-MS) to quantify gaseous product generation during electrochemical testing. As a function of electrocatalysis, time, gas-type saturation, and Co2+ concentration, we observe windows of Co stability that are different than thermodynamically projected, suggesting new stabilization and degradation mechanisms. In particular, Co is an active electrocatalyst for the hydrogen evolution reaction (HER) with an onset potential of -0.1 VRHE and prolonged material stability that is ∼300 mV greater than thermodynamically expected. Additionally, when exposed to an oxygenated environment, Co performs the HER and the oxygen reduction reaction (ORR) concurrently, yet the Co surface undergoes different morphology changes and dissolution mechanisms. When at open-circuit voltage, there is a 22× decrease in Co dissolution in an oxygen-free environment, which can be leveraged to decrease Co losses during device shutdown protocols. Lastly, when exposed to a positive and wide potential window (0.2 to 1.55 VRHE), the Co surface becomes stable after a substantial amount of dissolution, likely due to a high concentration of Co2+ ions in the microenvironment promoting the formation of a stable CoHO2 surface. Altogether, the experimental platform and fundamental insights presented can be leveraged to improve the stability of Co-containing devices and materials, promote strategic strategies for prolonged material utilization, and ultimately provide new avenues to design and develop more robust and affordable sustainable energy technologies.
