MXenes earned their name from their layered MAX-phase parents, with M standing for transition metals such as titanium, vanadium, niobium, or molybdenum, X for carbon or nitrogen, and the suffix echoing graphene to signal a two-dimensional structure. First synthesized in 2011, when Ti3AlC2 particles were submerged in hydrofluoric acid to strip out the aluminum layers, these accordion-like multilayer sheets can be delaminated into thin, transparent nanosheets with enormous surface area. Unlike graphene or carbon nanotubes, which rely mainly on electrostatic charge storage and often require extra functionalization, MXenes combine intrinsic metallic conductivity with hydrophilic surfaces decorated with oxygen, hydroxyl, and fluorine terminations. That combination enables pseudocapacitive charge storage, rapid ion transport, and strong interfacial bonding with metals, sulfides, phosphides, and semiconductor partners.

The review devotes considerable attention to synthesis, because the production route largely dictates surface chemistry and electrochemical behavior. Hydrofluoric acid etching remains the classical method, but safer in situ etching using fluoride salts with hydrochloric acid, hydrothermal etching in sealed autoclaves, solvothermal processing, electrochemical etching, and fluorine-free molten salt routes have all expanded the toolkit. Lewis acidic molten salt etching with zinc chloride, for example, can produce chlorine-terminated MXenes with controlled surface chemistry, while microwave-assisted approaches can deliver MXenes in minutes. The authors stress that no single fabrication strategy satisfies every requirement for practical electrodes, so rational matching of synthesis technique to application remains essential.

On the energy-storage front, MXene-based supercapacitors have progressed dramatically since the first demonstration in 2013. A binder-free Ti3C2Tx paper electrode produced by vacuum filtration achieved a volumetric capacitance of 350 F cm-3 in potassium hydroxide electrolyte, matching advanced graphene systems, and later LiF/HCl-etched clay films pushed volumetric capacitance to roughly 900 F cm-3. Composite engineering has multiplied these gains. Manganese dioxide nanowhiskers grown directly on MXene surfaces delivered around 212 F g-1 with 87.7% retention after 10,000 cycles, while MXene/PANI hybrids fabricated through oxidant-free in situ polymerization reached approximately 503 F g-1 and 1682 F cm-3, retaining 98.3% of their capacitance after 10,000 cycles even at thick, high-mass-loading electrodes. Sandwich-like heterostructures combining bimetallic sulfides with Ti3C2Tx have reported specific capacitances as high as 2637 F g-1 and device-level energy densities near 80 Wh kg-1.

These performance leaps rest on a charge-storage mechanism that uniquely blends electric double-layer capacitance with fast, reversible surface redox reactions. Electrolyte ions adsorb onto the conductive MXene sheets while the terminal groups mediate Faradic processes involving protons or alkali-metal cations. In acidic media, proton-coupled surface redox dominates; in neutral and alkaline electrolytes, hydrated cation intercalation between expanded interlayers becomes the key factor. Strategies such as interlayer pillaring, which can widen the spacing to 3.2 nanometers, heteroatom doping, defect engineering via plasma-assisted mechanochemistry, and deliberate vacancy creation in vanadium-based MXenes all enhance ion accessibility and active-site density, though excessive defects can compromise structural stability.

The second half of the review turns to electrocatalytic water splitting, where water is decomposed into hydrogen and oxygen through the hydrogen evolution reaction at the cathode and the more sluggish four-electron oxygen evolution reaction at the anode. Theoretical work indicates that oxygen-terminated MXenes approach the ideal near-zero hydrogen adsorption free energy required for efficient HER. Experimental systems have validated this promise: a platinum-anchored vanadium carbide MXene achieved a 27 mV overpotential at 10 mA cm-2 with a Tafel slope of 36.5 mV dec-1, while ruthenium-incorporated cobalt phosphide on MXene delivered overpotentials of just 9 mV in alkaline media and about 97% voltage retention over 200 hours. Molybdenum disulfide quantum dots on Ti3C2Tx, Ru single atoms and clusters on molybdenum carbide MXene, and nitrogen-doped Ti2CO2 designed through density functional theory all illustrate how MXene supports accelerate charge transfer and water dissociation.

For oxygen evolution, MXenes excel primarily as conductive, stabilizing supports for catalytically active species. High-entropy oxides grown on MXene nanosheets by rapid microwave heating produced a Tafel slope of 71 mV dec-1 and strong photoelectrochemical activity, whereas bimetallic NiFe-Ti3C2Clx MXene hybrids formed through molten salt synthesis reached 310 mV overpotential with Ni centers identified as the dominant active sites. Metal-organic-framework-derived nickel-cobalt sulfide on ultrathin MXene sheets and oxygen-vacancy-engineered FeOOH arrays on Ti3C2Tx, the latter outperforming commercial iridium oxide in stability tests exceeding 100 hours, underscore how heterostructure and doping strategies convert MXene limitations into synergistic advantages.

Perhaps the most commercially consequential advance involves bifunctional electrocatalysts that perform both HER and OER in a simplified two-electrode electrolyzer. Triple-interface Ni3Se4-NiSe2-Co3O4 heterostructures on MXene reached 100 mA cm-2 at a cell voltage of only 1.64 V with 100 hours of stable operation, while L-tryptophan-anchored CoNi-Ti3C2Tx split water at 1.58 V and sustained an industrially relevant 500 mA cm-2 at 1.87 V in an anion-exchange membrane electrolyzer. Ultrafine ruthenium-cobalt nanoparticles on MXene required just 1.52 V with near-100% Faradaic efficiency, and a low-cost multi-hybrid MXene/Mn3O4/CuO composite maintained stability for twelve days. The authors argue these systems bridge the gap between laboratory metrics and real-world hydrogen production.

Significant hurdles remain before MXene technologies reach the market. Oxidation instability remains the foremost concern, as pristine nanosheets degrade in air, water, and light, converting conductive carbides into insulating titanium dioxide and eroding capacitance. Nanosheet restacking suppresses ion transport, hydrofluoric acid etching raises environmental and scalability questions, surface terminations are difficult to control reproducibly, and precursor costs complicate mass production. Countermeasures are maturing rapidly, including edge capping with polyanionic salts, cold storage under inert conditions, polymer encapsulation, and three-dimensional aerogel architectures. Looking ahead, the review calls for green etching chemistry, defect and interface engineering, machine-learning-guided materials discovery, solid-state and wearable supercapacitor designs, and stronger academia-industry collaboration to carry MXenes from the laboratory bench toward sustainable energy storage and industrial-scale clean hydrogen generation.

Subject of Research: MXene nanomaterials for next-generation supercapacitors and electrochemical water splitting

Article Title: Recent advances of MXene as a frontier nanoarchitecture in energy science for shaping the future of next-generation supercapacitor and water splitting technology

Article References: Sau, A., Hassan, T., Mitra, S., Ghosh, S., Basu, R., & Das, S. (2026). Recent advances of MXene as a frontier nanoarchitecture in energy science for shaping the future of next-generation supercapacitor and water splitting technology. Discover Electrochemistry, 3(1), Article 70. https://doi.org/10.1007/s44373-026-00156-9

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00156-9

Keywords: MXene, supercapacitors, water splitting, hydrogen evolution reaction, oxygen evolution reaction, two-dimensional materials, energy storage, electrocatalysis, pseudocapacitance, heterostructures, surface functionalization, green hydrogen