Trivalent chromium conversion coatings

An Industrially Applicable Passivation Strategy for Significantly Improving Cyclability of Zinc Metal Anodes in Aqueous Batteries

“…In sharp contrast, native Cr(III) oxides in TCCF show superior Zn affinity, as binding en-ergies of Zn-CrOOH(104), Zn-Cr 2 O 3 (101), Zn-Cr 2 O 3 (116), and Zn-Cr 2 O 3 (104) were −0.82, −0.78, −1.02, and −1.42 eV, respectively.Meanwhile, these adsorption energy values for TCCF are within the appropriate range and comparable to the reported values for indium tin oxide protection layers,[49] which achieve simultaneous strong zincophilicity and fast Zn 2+ ion migration. The present analyses of the theoretical calculations agree with the experimental results on the zincophilicity of Cr and its native oxides [36,50]. Such strong zincophilicity of the TCCF provides abundant anchor sites for the Zn 2+ ion desolvation and Zn nucleation and limits rampant Zn diffusion and severe Zn nuclei aggregation, promising significantly improved cyclability of ZMAs.…”

“…The present analyses of the theoretical calculations agree with the experimental results on the zincophilicity of Cr and its native oxides. [36,50] Such strong zincophilicity of the TCCF provides abundant anchor sites for the Zn 2+ ion desolvation and Zn nucleation and limits rampant Zn diffusion and severe Zn nuclei aggregation, promising significantly improved cyclability of ZMAs. Then, the mechanism for Zn deposition on dendrite-free ZMAs with TCCF as the artificial interphase is schematically described in Figure 2c.…”

“…The as‐deposited TCCF on the ZMAs abide by a well‐accepted formation mechanism previously reported in the literature. [ 36 ] In brief, surface Zn atoms are oxidized to Zn 2+ ions by dissolved oxygen and H + ions, which increase the interfacial pH and generate hydroxides. Then, the local hydroxides react with the existing Cr 3+ ions to form native Cr(III) oxides.…”

“…For decades, TCCF have demonstrated outstanding corrosion resistance for various sacrificial coatings, including Zn and its alloys, during the protection of underlying metals such as steels. [36,38,39] Significantly, the low-toxicity TCCF exhibit zincophilicity, wettability, and an electronically insulated nature, [36] which are beneficial for suppressing Zn dendrite generation and alleviating parasitic side reactions that take place on the surface of Zn foils. [40][41][42][43][44][45][46] If superior passivation films can be converted into artificial interphases, diverse Zn plating passivation strategies might greatly stimulate the progress of surface modification approaches for Zn anode protection.…”

“…Industrially, the functional lifespan of Zn-plated steels is often prolonged by passivation films formed in situ on the surface of Zn coatings through a passivation treatment, involving simple immersion into a specific passivation solution. [36][37][38][39] Take the commercially available Cr(III)-based passivation technique as an example, the physically protective properties of trivalent chromium conversion films (TCCF) can be controlled by tuning the composition of the passivation bath, including the film former, oxidizer, inhibitor, sealant, surfactant, etc. [36,38,39] The asprepared TCCF with adjustable colors (e.g., black, bright blue, green, and colorful) are typically comprised of a complex mixture containing Cr(III) oxides, hydroxides, and hydrated oxides.…”