The corrosive anions (e.g., Cl⁻) have been recognized as the origins to cause severe corrosion of anode during seawater electrolysis, while in experiments it is found that natural seawater (~0.41 M Cl⁻) is usually more corrosive than simulated seawater (~0.5 M Cl⁻). Here we elucidate that besides Cl⁻, Br⁻ in seawater is even more harmful to Ni-based anodes because of the inferior corrosion resistance and faster corrosion kinetics in bromide than in chloride. Experimental and simulated results reveal that Cl⁻ corrodes locally to form narrow-deep pits while Br⁻ etches extensively to generate shallow-wide pits, which can be attributed to the fast diffusion kinetics of Cl⁻ and the lower reaction energy of Br⁻ in the passivation layer. Additionally, for the Ni-based electrodes with catalysts (e.g., NiFe-LDH) loading on the surface, Br⁻ causes extensive spalling of the catalyst layer, resulting in rapid performance degradation. This work clearly points out that, in addition to anti-Cl⁻ corrosion, designing anti-Br⁻ corrosion anodes is even more crucial for future application of seawater electrolysis.

M_n+1AX_n (MAX) phases are a novel class of materials with a closely packed hexagonal structure that bridge the gap between metals and ceramics, garnering tremendous research interest worldwide in recent years. Benefiting from their unique layered structure and mixed covalent–ionic–metallic bonding characteristics, MAX phase coatings possess excellent oxidation resistance, and exceptional electrical and thermal conductivities, making them highly promising for applications in advanced nuclear materials, battery plate protection materials, and aero-engine functional materials. This review aims to provide a comprehensive understanding of MAX phase coatings. It presents an overview of their compositions and microstructure, highlighting well-established structures like 211, 312, and 413. Furthermore, it delves into the various synthesis methods employed in fabricating MAX phase coatings, including physical vapor deposition, chemical vapor deposition, spraying methods, and laser cladding, among others. The potential applications of MAX phase coatings, high-temperature oxidation resistance, mechanical protection, salt spray corrosion resistance, etc., are also investigated. Finally, this review discusses the future potential of MAX phase coatings and proposes areas for further research and improvement. The primary goal is to offer theoretical guidance and innovative ideas for the synthesis and development of superior MAX phase coatings for commercial applications.