A Defective PtCoO₂ 2D Conductor with Resistivity Lower than Pt: Design of Molten Salt Synthesis

Highly defective 2D layered molten salt synthesized polycrystalline PtCoO₂ is metallic down to 1.8 K with a resistivity of 1.36 ± 0.05 μΩ·cm at 300 K, which is an order lower than that of Pt. The design of NaCl-CoCl₂ molten salt and its chemistry for obtaining phase-pure PtCoO₂ are presented. Dynamic changes in liquidus temperatures brought about by the compositional changes of NaCl-CoCl₂ upon consumption of CoCl₂ during the reaction are constrained to be within ±35 °C by a predesigned salt mixture. Rietveld structural refinements of XRD and SAED confirm the R3̅m space group with predominant (00l) texturing. XPS reveals that Co and Pt are predominantly in +3 and +1 oxidation states, respectively. PtCoO₂ is paramagnetic due to the low-spin Co⁴⁺, which undergoes antiferromagnetic ordering around 14 K. The catalytic property of PtCoO₂ is investigated for H₂ sensing.