Nanoscale, impurity-based, surficial films with self-selecting or “equilibrium” thickness can form spontaneously as the thermodynamic equilibrium states in various oxide materials [Annu. Rev. Mater. Res. 38: 227 (2008)]. They can be considered as a unique class of 2-D surface phases (that are also called “complexions” to differentiate them from the 3-D bulk phases defined by Gibbs). Such surface phases can be utilized as a class of ideal nanocoatings (made by thermodynamics) to improve the performance of various functional materials for energy-related applications. This presentation will review a series of our recent studies to utilize this and other analogous types of spontaneously-formed 2-D surface phases to tailor battery cathode [APL 95: 211905 (2009); JCCP 16: 7786 (2014)] and anode [J. Power Source 245: 594 (2014)] materials, supported oxide catalysts [APL 91: 061909 (2007); Acta Mater. 56: 4702 (2008)] and photocatalysts [Mater. Lett. 98: 205 (2013)], nanowire-based fast oxygen-ion conductors [Nature Communications 6: 8354 (2015)], and supercapacitors [unpublished results]. A potentially-transformative scientific goal is to utilize such 2-D surface phases to achieve superior properties that are unattainable by conventional bulk phases.