www.advmatinterfaces.de the sessile CA remains the favored method for quantifying wettability, mostly due to its conceptual and measurement simplicity. [9,31] However, the classification on the basis of the cut-off CA of 90° has attracted criticism. [32,33] The simplistic evaluation criteria of relative wettability are becoming inadequate in satisfying the needs of superwettability studies to classify different wetting phenomena. [34] Several works have questioned the accuracy of the sessile-droplet measurement as the CA value approaches the limits of 0° or 180°. [35,36] Yet, evaluation of surfaces in the superhydrophobic (CA > 150°) and superhydrophilic (CA < 10°) regimes is central in the development of enhanced wettabilities. Moreover, the interpretation of the CA results is often complicated by several factors, including surface smoothness, heterogeneity and cleanliness. [37] The Chun Haow Kung obtained his B.A.Sc. and M.A.Sc. in Chemical Engineering at the University of British Columbia (UBC). His graduate work with Prof. Mérida's group at UBC focused on the development and application of novel wetting characterization techniques, smart stimuli-responsive materials as well as electrochemical and hydrogen energy systems. He is currently a Research Scientist at Ballard Power Systems Inc. where he continues to pursue his interest in the polymer electrolyte membrane (PEM) fuel cell technology. Beniamin Zahiri is currently a researcher in the University of Illinois at Urbana-Champaign

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Fast and reversible active control over the surface wettability of electrodeposited copper is achieved through electrochemical manipulation of the oxidation state. The switchable wettability described in this work allows for facile and precise control over the surface wettability, ranging from superhydrophobic (contact angle about 157°) to superhydrophilic (contact angle less than 10°) with a short response time. The rate of wetting transition and the desired contact angle can be precisely controlled by modulating the magnitude and duration of the applied potential. The wettability alteration is completely reversible when the sample is dried at ambient or heat‐dried at 100 °C. The heat‐drying does not impact the surface composition when compared to the samples dried at room temperature. The surface contains a mixture of CuO and Cu2O as revealed by the surface composition analysis. The mechanism underlying the wetting alteration is based on the Faradaic phase transformation at the surface. An integrated droplet manipulation system is also demonstrated. The single‐step and additive‐free sample preparation is scalable and can be used to design smart surfaces and devices that require control over the wettability (e.g., liquid lenses, microfluidic devices, sensitive particulate matter handling systems, controlled filtration, and biomedical applications).