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Metallic delafossites ABO2, as the new benchmark of ultra‐high conductive oxides, have recently attracted great interest. The harsh processing conditions and dimensional sizes obviously limit the fundamental sciences and technological applications. Here, a low‐cost and facile solution approach is realized to synthesize epitaxial metallic ABO2 thin films including PtCoO2, PdCoO2, and PdCrO2 with a dimension up to two‐inches in diameter, showing ultra‐high room temperature conductivity. The electrical properties, growth mechanisms, and potential technical applications including transparent conducting films and hydrogen evolution reaction activity are unveiled. The achievements of epitaxial metallic delafossites ABO2 thin films through solution methods will pave the route to producing wafer‐scaled ultra‐high conductive metallic delafossites. [ABSTRACT FROM AUTHOR]

Photocatalytic hydrogen evolution technology is recognized as a promising approach to relieving the growing energy crisis. Therefore, the development of a stable high‐performance photocatalyst has long been the focus of research. In this work, quaternary composite materials involving a snowflake‐like CdS nanocrystal wrapped by different amounts of polyoxometalate‐decorated g‐C3N4 and polypyrrole (GPP@CdS) have been synthesized as photocatalysts for hydrogen production under visible‐light irradiation. It has been revealed that the best composite (40 % GPP@CdS composite) exhibits hydrogen production activity of 1321 μmol, which exceeds that of CdS by a factor of more than two, and can be used in at least seven cycles with negligible loss of activity. The enhanced photocatalytic performance has been primarily attributed to the efficient synergy of CdS, g‐C3N4, polypyrrole (PPy), and the polyoxometalate Ni4(PW9)2. It should be noted that the introduction of PPy and g‐C3N4 into the title composite simultaneously promotes electron/hole pair separation and photocatalytic stability, whereas Ni4(PW9)2 serves as an efficient electron modulator and extra catalytic active site. Synergy in action. A novel polyoxometalate‐decorated g‐C3N4‐wrapping snowflake‐like CdS nanocrystal photocatalyst, by virtue of the synergistic effect stemming from the integration of the individual advantages of CdS, g‐C3N4, polypyrrole, and the polyoxometalate Ni4(PW9)2, displays high‐performance hydrogen production activity and superior photocatalytic stability (see figure). [ABSTRACT FROM AUTHOR]