Photoelectrocatalysis of CaCd₂P₂—A Case Study in Novel Ternary Zintl Phosphides for Solar Fuel Production

No known solar fuel photo(electro)catalyst displays the intersection of high-performance, stability, strong absorption, and Earth abundance necessary for deployment at scale. These ongoing challenges present an urgent need for discovery of new material candidates. Ternary Zintl phosphides, with an AM₂P₂ composition, have recently been identified in computational discovery efforts for solar energy conversion applications.¹ Continued computational screening has identified many AM₂P₂ family members as having promising optoelectronic properties with stabilities suitable for synthesis and solar energy conversion. Here, we introduce the synthesis and photoelectrochemical characterization of the first material of photocatalytic interest originating from these efforts, CaCd₂P₂ (CCP). CCP exhibits intense optical absorption and a predicted direct bandgap of 1.62eV, corroborated by strong band-to-band photoluminescent emission at ~1.6eV. In water splitting measurements under simulated 1-sun illumination, as-synthesized CCP powder demonstrates photoelectrochemical activity for both hydrogen and oxygen evolution, as well as robust stability in alkaline conditions. Its photocatalytic potential, stability, and semiconducting properties will be discussed, as well as opportunities for further discovery and solar fuels development in this new Zintl phosphide family of materials.<br/><br/>[1] Yuan, Zhenkun, et al. "Discovery of the Zintl-phosphide BaCd2P2 as a long carrier lifetime and stable solar absorber." <i>Joule</i> 8.5 (2024): 1412-1429.