The ability of transition metal atoms to reversibly change the oxidation state enables redox energy storage. Catalytic properties of some of the transition metals lead to use of their oxides in catalysis and electrocatalysis. A few oxides that are conductive find applications in transparent conductive layers in solar cells, thus contributing to energy harvesting. However, the majority of oxides have a low conductivity, limiting their applications in electrocatalysis, electrochemical energy storage, harvesting, and conversion. Two-dimensional (2D) carbides and nitrides of transition metals known as MXenes, with a thickness of a nanometer or less, have their surfaces terminated by oxygen or OH, forming compounds like Mo₂CO₂, Ti₃C₂(O,OH)_x, or Nb₄C₃O₂ with the surfaces resembling that of oxides or hydroxides. They are hydrophilic, form stable colloidal solutions in water, and work well with aqueous, ionic liquid or polar organic electrolytes. They chemically behave very much like the corresponding oxides/hydroxides; however, the fundamental difference is that electrons of the transition metal give them metallic conductivity, thus compensating for the key limitation of oxides and eliminating the need for conductive carbon additives. Moreover, the conductivity of titanium carbide MXene with O, OH, and/or F terminated surface is outstanding and can exceed 20,000 S/cm. A combination of high electronic conductivity with hydrophilicity and 2D structure facilitates electronic and ionic transport, allowing extremely fast charge/discharge with the electron transfer. Naturally, this opens new opportunities in energy storage, electrocatalysis, and other fields where a combination or surface redox with electrical conductivity is required. The family of 2D transition metal carbides and nitrides (MXenes) has been expanding rapidly since the discovery of Ti₃C₂T_x (T stands for surface terminations) in 2011 [1]. Approximately 30 different stoichiometric MXenes have been synthesized, and the structures and properties of numerous other MXenes have been predicted using density functional theory (DFT) calculations [2]. Furthermore, the availability of solid solutions on M and X sites, control of surface terminations, and the discovery of in-plane and out-of-plane ordered double-M MXenes (e.g., Mo₂TiC₂T_x) offer a potential for synthesis of dozens if not hundreds of new materials. The versatile chemistry of the MXene family renders their properties (conductivity, work function, surface charge, etc.) tunable for a large variety of catalytic and energy-related applications. Particularly, they are very promising candidates for energy storage [2], but applications in electrocatalysis, transparent conducting layers, biosensors, capacitive water desalination, and other fields are equally exciting [3].