Advancing Hydrogen Production with MXenes in Water Splitting

Hydrogen is becoming an increasingly important energy source. This growing demand highlights the need for sustainable, clean, and efficient hydrogen production methods—particularly water splitting.

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Electrocatalysts play a key role in enabling hydrogen generation through water splitting. Among the latest materials under investigation, two-dimensional (2D) materials known as MXenes have shown strong potential for clean hydrogen production.

This article explores how MXenes are used across different water splitting approaches to improve efficiency and advance hydrogen generation technologies.

What are MXenes?

MXenes are a family of two-dimensional (2D) materials composed of transition metal carbides, carbonitrides, or nitrides. They are typically represented by the general formula M_n+1X_nT_x, where:

• M is a transition metal (typically from groups 3 to 6 of the periodic table),
• X is carbon and/or nitrogen
• and Tx represents surface terminations, such as oxygen, hydroxyl, or halogens (from groups 16 or 17 of the periodic table).¹

Electrocatalytic Applications of MXenes

Electrochemical water splitting is a sustainable and eco-friendly method for producing clean hydrogen. MXenes have emerged as promising electrocatalysts, particularly for the hydrogen evolution reaction (HER).

In a typical electrolysis setup, the oxygen evolution reaction (OER) occurs at the anode, while HER takes place at the cathode. In acidic media, HER proceeds via Volmer’s reaction (proton adsorption), followed by either the Heyrovsky (electrochemical desorption) or Tafel (recombination) step.

In alkaline conditions, where free protons (H⁺) are absent, water molecules first dissociate to provide protons, and the mechanism continues similarly.²

MXenes, such as Ti₂CT_x, have shown excellent catalytic activity in acidic conditions. For example, Li et al. used Ti₂CT_x in a 0.5M H₂SO₄ solution, where T_x represents surface terminations like oxygen, hydroxyl, or fluorine. The fluorinated Ti₂CT_x demonstrated a low overpotential of 75 mV and a Tafel slope of 100 mV/dec.³

Mo₂CT_x, another MXene variant, has demonstrated greater stability and catalytic performance than Ti₂CT_x in acidic environments. A study by Zhi et al. reported an initial overpotential of 283 mV for Mo₂CT_x with only minimal performance loss after 30 cycles—outperforming traditional catalysts.⁴

MXenes have also been used to form nanocomposites with other materials, further enhancing catalytic efficiency. Their surface terminations make them ideal for forming MXene–TMD (transition metal dichalcogenide) nanohybrids, such as those with MoSe₂ or MoS₂. These hybrids offer superior charge transport and more active sites for hydrogen adsorption, leading to improved HER efficiency compared to conventional catalysts.⁵

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Photocatalytic and Photoelectrochemical Applications of MXenes

The drive for low-carbon hydrogen production has accelerated research into photocatalysis and photoelectrochemical (PEC) water splitting, where solar energy is used to drive the redox reactions involved in water dissociation. MXenes are increasingly being explored in this space due to their light absorption and charge mobility properties.

Studies have shown that 2D MXenes such as Zr₂CO₂ and Hf₂CO₂ can act as effective photocatalysts. These materials absorb both visible and UV light and exhibit high carrier mobility, which is essential for efficient photocatalytic activity.

These MXenes display anisotropic carrier mobility, where electrons preferentially move along the y-axis and holes migrate along the x-axis. This directional separation of charge carriers helps suppress recombination and enhances the migration of photo-generated electron-hole pairs, significantly improving photocatalytic efficiency.⁶

For photoelectrochemical water splitting, MXenes are used not only as active photoelectrodes but also as co-catalysts to improve charge separation and suppress recombination. One example is a 2D nanocomposite consisting of ZnO and Ti₃C₂T_x photoanode, created by spin-coating Ti₃C₂T_x onto a ZnO photoanode.

This hybrid photoanode achieved a photocurrent density of 1.2 mAcm^-2—approximately 1.4 times higher than ZnO alone—and maintained a stable photocurrent over 2000 seconds. The incorporation of MXene flakes improved charge transfer kinetics and boosted the overall efficiency of the PEC water-splitting process.⁷

Performance Benefits of MXenes in Hydrogen Generation

Experimental studies have demonstrated that MXenes can accelerate water-splitting reactions and increase hydrogen output, all while producing fewer emissions. Their distinct properties—such as hydrophilic surface terminations, high surface-to-volume ratios, and structural flexibility—make them highly effective as catalysts.

MXenes can also be tailored for specific water-splitting approaches through strategies like end-group modification, heterojunction formation, and nanostructural engineering.

MXene-based catalysts have consistently shown lower overpotential values for the HER, boosting catalytic performance and hydrogen production beyond that of conventional noble-metal-based catalysts.⁸

Additionally, their excellent metallic conductivity, large specific surface area, and favorable hydrophilicity further enhance their efficiency in water-splitting applications.⁹

Current Limitations and Barriers to MXene Adoption

Although MXenes show strong potential for water-splitting and hydrogen production, several challenges limit their practical application. One key issue is their susceptibility to oxidation during electrocatalytic reactions, which leads to catalytic deactivation.

Studies have shown that in materials like Ti₃C₂T_x, oxidation begins at the edges and progresses inward, significantly reducing their electrochemical activity.

Another limitation is the tendency of MXenes to aggregate during electrode preparation, which decreases the number of exposed active sites. Additionally, their intrinsic catalytic activity is relatively low, often requiring hybridization with other materials to enhance performance.

Oxidative degradation remains a persistent problem. In the presence of water, oxygen reacts with active MXene edges, forming TiO₂ and causing structural deformation that impairs catalytic efficiency.

Furthermore, the high surface energy of MXenes leads to restacking, which reduces their catalytic efficiency for splitting H₂O into hydrogen. Large-scale industrial production also remains a challenge—it is costly, technically complex, and constrained by synthesis processes that require specialized materials and conditions not well-suited to mass manufacturing.¹⁰

Overcoming these barriers will require continued research into more stable and diverse MXene formulations. This includes exploring novel materials such as V-based MXenes and double transition metal MXenes to expand their functional range.

Improving the stability of MXenes will also depend on optimizing MAX phase synthesis to produce low-defect precursors. Developing stable heterostructures is essential for preserving active sites and maintaining long-term catalytic performance.

These advancements will be key to scaling MXene-based water splitting technologies and unlocking their full potential in clean hydrogen production and renewable energy systems.

For more information on hydrogen production and advanced materials in water splitting, explore:

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References and Further Reading

1. Anasori, B., et al. (2022). MXenes: trends, growth, and future directions. Graphene and 2D mater. https://doi.org/10.1007/s41127-022-00053-z
2. Zhai, Y., et al. (2021). High density and unit activity integrated in amorphous catalysts for electrochemical water splitting. Small Structures. Available at: https://doi.org/10.1002/sstr.202000096
3. Li, S., et al. (2018). Ultrathin MXene nanosheets with rich fluorine termination groups realizing efficient electrocatalytic hydrogen evolution. Nano Energy. https://doi.org/10.1016/j.nanoen.2018.03.022
4. Seh, Z., et al. (2017). Two-dimensional molybdenum carbide (MXene) as an efficient electrocatalyst for hydrogen evolution. ACS Energy Lett. Available at: https://doi.org/10.1021/acsenergylett.6b00247
5. Sharma, M., et al. (2020). 2D Thin Sheet Heterostructures of MoS2 on MoSe2 as Efficient Electrocatalyst for Hydrogen Evolution Reaction in Wide pH Range, Inorg. Chem.https://doi.org/10.1021/acs.inorgchem.9b03445
6. Guo, Z., et al. (2016). MXene: a promising photocatalyst for water splitting. Journal of Materials Chemistry A. Available at: https://doi.org/10.1039/C6TA04414J
7. Zhong, C., et al. (2023). Co-Catalyst Ti3C2TX MXene-Modified ZnO Nanorods Photoanode for Enhanced Photoelectrochemical Water Splitting. Top Catal 66. https://doi.org/10.1007/s11244-022-01619-0
8. Pandey, S., et al. (2024). Value addition of MXenes as photo-/electrocatalysts in water splitting for sustainable hydrogen production. Chemical Communications. https://doi.org/10.1039/D4CC01811G
9. Salmasi, M., et al. (2024). MXenes as electrocatalysts for hydrogen production through the electrocatalytic water splitting process: A mini review. Energy Reviews. https://doi.org/10.1016/j.enrev.2024.100070
10. He, L., et al. (2024). Advances and challenges in MXene-based electrocatalysts: unlocking the potential for sustainable energy conversion. Materials Horizons. https://doi.org/10.1039/D4MH00845F

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