Electrocatalytic activity, phase kinetics, spectroscopic advancements, and photocorrosion behaviour in tantalum nitride phases

The search for sustainable energy solutions has led to extensive research on new electrocatalysts that can convert electrical energy into chemical energy and back. Tantalum nitrides stand out as an intriguing class of materials, showcasing exceptional properties such as high melting points, remarkable mechanical strength, and notable resistance to corrosion. These attributes position tantalum nitrides (Ta-N) and allied phases (Ta-N-X) as compelling candidates for diverse applications, notably in electrocatalysis. While traditionally studied for their photocatalytic and photoelectrocatalytic properties, this review ventures into largely uncharted territory, illuminating the untapped potential of tantalum nitrides as electrocatalysts. Electrocatalysis assumes a pivotal role in numerous renewable energy technologies, including fuel cells and water electrolysis, which demand materials adept at catalyzing reactions efficiently. The distinctive characteristics of Ta-N phases, particularly their electrical conductivity, chemical stability, and expansive surface area, mark them as promising contenders in this arena. This comprehensive review article aims to unveil the electrocatalytic prowess of Ta-N phases, examining their catalytic performance concerning the Hydrogen Evolution Reaction (HER), Oxygen Evolution Reaction (OER), and Oxygen Reduction Reaction (ORR). Delving into recent advancements over the past five years, the article scrutinizes strategies employed to counter surface oxidation - a prevailing degradation issue that hampers activity in Ta-N phases. It also describes methodologies to mitigate photocorrosion observed during photocatalytic/photoelectrochemical (PEC) water splitting of Ta-N phases, offering potential blueprints for efficient design of their electrocatalytic counterparts. The exploration encompasses a thorough investigation into the role of various correlative spectroscopy techniques, including X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and Fourier-Transform Infrared Spectroscopy (FTIR), in unraveling the involvement of oxygen-related species within Ta-N systems. Furthermore, the presence of oxygen necessitates an intricate comprehension of the thermodynamic stability of different Ta-N phases, both in the presence and absence of oxygen. This article underscores the importance of an exhaustive phase diagram analysis for the Ta-N system in the context of water splitting, critically evaluating thermochemical and constitutional data. Despite extensive research efforts, the phase diagram of the Ta-N system remains incomplete, restraining our understanding of phase stability and overall performance. This account aims to enhance understanding of Ta-N phases and provide insights that support cohesive electrocatalyst design, focusing on the key issue of long-term stability in electrocatalysis.