Oxygen Evolution Reaction with CaCd­₂P₂: A Case Study in Novel Ternary Zintl Phosphides for Solar Fuel Production

No known solar fuel electrocatalyst 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, 2]. 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 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 shows a notable photocurrent and photovoltage as well as robust stability under oxygen evolution reaction conditions (0.1M KOH, 2 V_RHE), owing to passivating surface transformation. The photocatalytic potential of CCP, semiconducting properties, nature of its passivating layer, and performance alongside a cocatalyst will be discussed, as well as opportunities for further discovery and solar fuels development in this new Zintl phosphide family of materials.



[1] Z. Yuan et al., “Discovery of the Zintl-phosphide BaCd2P2 as a long carrier lifetime and stable solar absorber,” Joule, vol. 8, no. 5, pp. 1412–1429, 2024.

[2] S. Quadir et al., “Low-Temperature Synthesis of Stable CaZn2P2 Zintl Phosphide Thin Films as Candidate Top Absorbers,” Adv. Energy Mater., vol. 2402640, pp. 1–12, 2024.