Incidental and Intentional Transformation: Transition Metal Pnictide and Chalcogenide Electrocatalysts for Alkaline Hydrogen Evolution

Transition metal pnictides and chalcogenides (X-ides) have been studied as promising electrocatalysts for the alkaline hydrogen evolution reaction (HER). These materials often undergo dynamic transformations, either on their surface or within their bulk, occurring "incidentally" during the HER or "intentionally" through electrochemical activation. Current research shows that X-ides can remain unchanged, undergo oxidation or reduction, or transform into different X-ides with reduced X-ogen (i.e., chalcogen or pnictogen) to metal ratios compared to their original forms. In this Focus Review, we explore examples of these transformations for incidental and intentional cases, identify gaps in current knowledge, discuss divergent views on the nature of catalytically active species, and provide recommendations for more accurate identification of the active HER species in future studies.