The appeal of TMDs begins with their unusual structure. With the general formula MX2, where M is a transition metal such as molybdenum, tungsten, niobium, or tantalum and X is sulfur, selenium, or tellurium, each monolayer consists of a sheet of metal atoms sandwiched between two sheets of chalcogen atoms. Adjacent layers are held together only by weak van der Waals forces, which means bulk crystals can be peeled into single-atom-thick sheets. This architecture yields enormous surface-area-to-volume ratios, coordinatively unsaturated edge atoms with dangling bonds that serve as natural binding sites for reactive intermediates, and interlayer galleries that can host rapid ion transport. These are precisely the features that electrochemical energy devices demand.

Yet pristine TMDs carry intrinsic handicaps. The thermodynamically stable 2H phase is semiconducting, which limits charge transport; the basal plane is chemically inert and contributes little to catalysis; and narrow interlayer spacing slows ion intercalation. Exfoliated nanosheets also tend to restack during device fabrication, degrading stability and cycling performance. The review’s central message is that these limitations are not dealbreakers but design opportunities, addressable through a toolkit that includes defect engineering, heteroatom doping and alloying, strain engineering, atomic-scale modulation, nanostructure design, interlayer and phase control, and heterostructure fabrication.

Defect engineering has proven especially powerful. Sulfur vacancies in molybdenum disulfide create donor states within the band gap and expose undercoordinated metal atoms that bind hydrogen favorably. One highlighted study used high-throughput density functional theory calculations to identify the optimal vacancy configuration, then developed a hydrogen peroxide chemical etching method to distribute single sulfur vacancies uniformly across MoS2 nanosheets. The resulting catalyst achieved a hydrogen evolution overpotential of just 131 millivolts at 10 milliamperes per square centimeter, with a Tafel slope near 48 millivolts per decade and excellent stability. The authors caution, however, that defects cut both ways: they can also act as scattering centers and trap states that degrade carrier mobility, so passivation of harmful defects must accompany the deliberate introduction of useful ones.

Doping and alloying offer complementary control over electronic structure. When researchers doped MoS2 with zinc using a fusion heat method, X-ray photoelectron spectroscopy revealed binding energy shifts of roughly 0.47 and 0.40 electron volts for the Mo 3d and S 2p levels, indicating increased electron density that accelerates the hydrogen discharge step. Bimetallic strategies push further: cobalt-doped MoS2 works bifunctionally in both acidic and alkaline water splitting, while ruthenium doping wrapped in carbon nanotubes activates the otherwise inert 2H basal plane. Alloying enables continuous band gap tuning, with CVD-grown MoS2(1-x)Se2x films showing more than ten percent band gap modulation and quaternary alloys spanning 1.60 to 2.03 electron volts. Remarkably, doping can even trigger phase transitions, as rhenium concentrations above 40 percent stabilize the metallic 1T-prime phase of MoSe2.

Strain engineering adds another dimension. Because TMD monolayers can withstand more than 20 percent elastic distortion, mechanical deformation directly reshapes their band structure. Computational work predicted that only 0.3 to 3 percent uniaxial tensile strain converts 1H-MoTe2 into the quasi-metallic 1T-prime phase at room temperature, and experiments confirmed strain-induced band gap tuning in MoS2. The most striking results come from combining strain with vacancies: when sulfur vacancies in monolayer 2H-MoS2 were simultaneously strained, gap states shifted toward the Fermi level, yielding near-optimal hydrogen adsorption free energy. The combined system showed a Tafel slope of 60 millivolts per decade versus 98 for pristine MoS2, and the turnover frequency of its molybdenum atoms exceeded even that of conventional edge sites.

Phase engineering targets the most consequential lever of all. The metallic 1T phase of MoS2 conducts electricity roughly ten million times better than the semiconducting 2H phase and is hydrophilic, both critical for electrochemistry. Chemically exfoliated 1T-MoS2 reaches benchmark hydrogen evolution current densities at around 187 to 195 millivolts versus RHE, compared with more than 300 millivolts for the 2H phase, with Tafel slopes dropping from about 110 to the mid-40s. Because 1T is metastable and reverts to 2H near 92 degrees Celsius, researchers have developed stabilization tricks including sulfur intercalation, metal cation insertion, and palladium doping that partially converts the phase and slashes Tafel slopes from 157 to as low as 62 millivolts per decade.

Heterostructures and single-atom catalysts round out the toolkit. Coupling MoS2 with WTe2 creates a low Schottky barrier at the interface that shortens electron transport paths from micrometers to roughly 700 picometers, dramatically improving charge injection. Covalent 0D-2D hybrids of Co9S8 nanoparticles bonded to MoS2 through Co-S-Mo links render molybdenum sites electron-rich and activate the basal plane across all pH values. Meanwhile, isolated nickel atoms anchored on MoS2 nanofibers cut hydrogen evolution overpotentials from 263 to 161 millivolts, and nickel-oxygen sites engineered onto 1T-MoS2 achieved an onset potential near 0 volts with an overpotential of only 46 millivolts in alkaline media. In photocatalysis, single-layer 1T-MoS2 paired with nitrogen-doped graphene produced hydrogen roughly 600 times faster than comparable 2H systems under visible light.

Energy storage results are equally compelling. Vertically aligned metallic MoS2 on graphene delivered initial lithium-ion capacities near 1700 milliampere-hours per gram, while carbon-free metallic nanotube anodes retained the 1T phase for at least 120 days in air. For sodium-ion batteries, freestanding 1T-MoS2 grown on hollow graphene foam sustained stable capacities around 313 milliampere-hours per gram over 200 cycles. Supercapacitors built from restacked 1T-MoS2 films achieved volumetric capacitances of 400 to 650 farads per cubic centimeter, retaining over 93 percent of initial capacitance after 5000 cycles, and water-coupled metallic MoS2 with nanochannels reached 150 farads per gram even without conductive additives. The review concludes that scalable synthesis, long-term phase stability, and clear structure-property correlations remain the key hurdles, and it points to artificial intelligence-assisted materials discovery as the accelerant that could carry these engineered atomically thin catalysts from laboratory demonstrations to industrial deployment.

Subject of Research: Materials engineering strategies for tuning metallic two-dimensional transition metal dichalcogenides for energy conversion and storage

Article Title: Recent advances in tuning the properties of metallic 2D transition-metal dichalcogenides for energy conversion and storage

Article References: Ha, J., Park, G., Kang, G., Kang, J., Bak, H., Lee, D., Lee, H., Cho, K., & Kim, Y. (2026). Recent advances in tuning the properties of metallic 2D transition-metal dichalcogenides for energy conversion and storage. Advances in Industrial and Engineering Chemistry, 2(1), Article 5. https://doi.org/10.1007/s44405-026-00045-0

Image Credits: AI Generated

DOI: 10.1007/s44405-026-00045-0

Keywords: transition metal dichalcogenides, two-dimensional materials, hydrogen evolution reaction, phase engineering, defect engineering, heteroatom doping, strain engineering, heterostructures, lithium-ion batteries, supercapacitors, electrocatalysis, energy storage