MXene-Enhanced Catalysts Pave the Way for Cost-Effective Green Hydrogen Production

Green hydrogen—hydrogen produced via water electrolysis powered by renewable energy—emerges as a cornerstone of a decarbonized future. It serves as both an energy carrier and a raw material, enabling industries to transition away from fossil fuels. By relying on electricity generated from solar or wind farms, green hydrogen production can be nearly climate-neutral. However, large-scale deployment faces a persistent challenge: the need for efficient, low-cost catalysts to drive the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at both electrodes of an electrolyzer. Until recently, precious metals such as iridium and platinum were the benchmarks for catalytic activity. Their scarcity and exorbitant cost impede the widespread adoption of green hydrogen. Consequently, research efforts have pivoted toward catalysts comprised of earth-abundant elements.

The Bottleneck: Oxygen Evolution Reaction and Catalyst Development
The rate-limiting step in water electrolysis is typically the OER at the anode, where four electrons must be transferred to oxidize water into oxygen. This multi-electron transfer is kinetically sluggish, necessitating catalysts that lower activation barriers and minimize energy losses. In current commercial electrolyzers, iridium oxide (IrO₂) and ruthenium oxide (RuO₂) serve as state-of-the-art anode catalysts. However, their limited supply and high market price—often exceeding $10,000 per ounce—render them impractical for the gigawatt-scale electrolysis necessary for climate goals. Platinum group metals at the cathode similarly raise obstacles. To make green hydrogen economically viable, researchers seek to identify new classes of catalysts that satisfy four criteria simultaneously:

1. High Activity: Catalytic performance comparable to, or exceeding, that of precious-metal benchmarks.
2. Stability: Electrochemical durability under harsh, highly oxidative conditions at the anode, and under alkaline or acidic pH during extended operation.
3. Low Cost: Based on abundant, inexpensive elements that are not geopolitically constrained.
4. Scalability: Synthetic pathways amenable to mass production without requiring rare precursors or costly processing.

MXenes as Catalyst Supports: A New Frontier
Keen to address the scalability challenge, the team at Helmholtz-Zentrum Berlin (HZB) turned its attention to MXenes—a family of two-dimensional transition metal carbides, nitrides, and carbonitrides. Discovered in 2011, MXenes possess formula Mₙ₊₁XₙTₓ, where M represents an early transition metal (e.g., titanium, vanadium), X is carbon or nitrogen, and Tₓ denotes surface terminations (–OH, –F, or –O) introduced during synthesis. Their hallmark properties include:

• Large Specific Surface Areas: The predominant “flaky” morphology yields an accessible surface that can host catalytically active species.
• High Electrical Conductivity: Electron mobility rivals that of conventional conductors, ensuring rapid charge transfer between embedded nanoparticles and the electrode.
• Tunability: By varying the transition metal M and synthesis conditions, MXene properties—surface chemistry, defect density, interlayer spacing—can be precisely controlled.

These features position MXenes as promising “support” materials that can anchor catalytically active nanoparticles. The rationale: by dispersing active metal or metal-oxide clusters on MXene sheets, one can achieve high particle dispersion (maximizing active sites), facilitate electron transport (improving turnover rates), and bolster mechanical and chemical stability (reducing catalyst degradation).

HZB’s MXene-Catalyst Breakthrough: From Concept to Reality
At HZB, a collaborative team led by Dr. Michelle Browne has developed a multi-step approach to produce hybrid catalysts based on MXene supports. Their recent publication in Advanced Functional Materials presents a rigorous study demonstrating that embedding cobalt-iron (CoFe) particles into vanadium carbide MXenes dramatically enhances OER activity compared to pure CoFe catalysts. Below, the key aspects of their approach and findings are detailed.

Vanadium Carbide MXene Variants and Vacancy Engineering
First author Dr. Can Kaplan, a doctoral candidate in Browne’s group, synthesized two variants of vanadium carbide MXene—an important subclass denoted by the formula V₂CTₓ and a vacancy-engineered variant V₁.₈CTₓ with 10% vanadium vacancies. These variants were prepared in collaboration with Prof. Lars Österlund’s group at Linköping University in Sweden, part of Kaplan’s Ph.D. exchange program. Linköping’s well-equipped facilities enabled the following steps:

1. Selective Etching: Starting from parent MAX phases (V₂AlC or V₄AlC₃), the team employed a modified hydrofluoric acid (HF) or lithium fluoride (LiF)/HCl etching process to remove the aluminum layers, yielding multilayered V₂CTₓ and V₁.₈CTₓ MXene phases.
2. Intercalation and Delamination: The etched products were treated with dimethyl sulfoxide (DMSO) or tetramethylammonium hydroxide (TMAOH) to expand interlayer spacing. Subsequent sonication in water yielded few-layer MXene colloids.
3. Vacancy Introduction: To achieve V₁.₈CTₓ, a partial thermal annealing under a reductive Ar/H₂ environment removed a controlled amount of vanadium atoms, creating approximately 10% metal vacancies. These vacancies translated into a significantly higher specific surface area—around 200 m²/g compared to 120 m²/g for vacancy-poor V₂CTₓ—thereby providing more anchoring sites for metal particles.

Embedding Co₀.₆₆Fe₀.₃₄ Nanoparticles: A Multi-Step Colloidal Approach
Once the MXenes were in hand, Browne’s group developed a robust, multi-step colloidal method to incorporate cobalt-iron nanoparticles into the MXene lattice:

1. Precursor Preparation: Aqueous solutions of cobalt (Co²⁺) and iron (Fe²⁺) nitrates were prepared at a molar ratio corresponding to Co₀.₆₆Fe₀.₃₄. This ratio was selected based on prior studies showing optimal OER activity for mixed‐metal oxides in alkaline conditions.
2. Adsorption onto MXene Surfaces: Delaminated MXene nanosheets were dispersed in deionized water to form a colloidal suspension. The Co²⁺/Fe²⁺ precursor solution was slowly added under vigorous stirring to ensure uniform adsorption of metal cations onto the MXene’s surface terminations (–OH and –O groups).
3. In Situ Co-precipitation: By raising the pH to 9–10 with sodium hydroxide (NaOH), the team induced in situ co-precipitation of a mixed hydroxide precursor (CoFe–LDH) directly onto the MXene surfaces. The stirring continued at ambient temperature for two hours to allow the hydroxide layers to uniformly nucleate.
4. Thermal Conversion to Oxide/Metal Phases: The MXene/hydroxide composite was collected by centrifugation, washed, and then subjected to a mild annealing step at 300 °C under a flowing H₂/Ar atmosphere. This treatment reduced hydroxides to metallic or oxide nanoparticles—depending on local redox microenvironments—while avoiding excessive oxidation of the underlying MXene.
5. Surface Passivation and Activation: A final brief thermal treatment in air at 200 °C furnished a thin oxide shell (CoₓFeₓO_y) atop the embedded metal core, which is known to enhance OER intermediate adsorption (OH⁻, OOH, and O₂) and improve long-term stability.

The entire process yielded Co₀.₆₆Fe₀.₃₄@V₂CTₓ and Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ hybrid catalysts with metal loadings around 30 wt%. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) images confirmed that CoFe nanoparticles—approximately 5–10 nm in diameter—were uniformly dispersed along the inner and outer MXene surfaces. Energy-dispersive X-ray spectroscopy (EDS) mapping demonstrated co-localization of Co, Fe, V, and C signals, indicating successful integration without significant phase separation.

Electrochemical Evaluation: A Step Change in OER Activity
To assess catalytic performance, the researchers employed standard three-electrode electrochemical cells in 0.1 M KOH, comparing four samples:

• Pure Co₀.₆₆Fe₀.₃₄ Nanoparticles (Powder)
• Co₀.₆₆Fe₀.₃₄@V₂CTₓ (Vacancy-Poor MXene)
• Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ (Vacancy-Rich MXene)
• Bare MXene Variants (V₂CTₓ and V₁.₈CTₓ)

Key findings included:

1. Overpotential Reduction: At a benchmark current density of 10 mA cm⁻² (roughly equivalent to solar-driven electrolysis goals), pure Co₀.₆₆Fe₀.₃₄ required an overpotential of 320 mV. When hybridized with V₂CTₓ, the overpotential decreased to 290 mV. Strikingly, embedding Co₀.₆₆Fe₀.₃₄ in V₁.₈CTₓ further reduced the overpotential to 270 mV—an improvement of 50 mV over the pure CoFe reference.
2. Tafel Slope: The Tafel slope indicates catalytic reaction kinetics. Pure Co₀.₆₆Fe₀.₃₄ recorded a slope of 72 mV dec⁻¹, whereas Co₀.₆₆Fe₀.₃₄@V₂CTₓ exhibited 65 mV dec⁻¹. The Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ variant achieved a 58 mV dec⁻¹ slope, approaching the ideal 40 mV dec⁻¹ associated with efficient OER mechanisms.
3. Electrochemically Active Surface Area (ECSA): Cyclic voltammetry (CV) in a non-faradaic region was used to estimate double-layer capacitance, from which ECSA was derived. Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ exhibited a capacitance roughly 2.5 times higher than the vacancy-poor variant, confirming that the increased vanadium vacancies translated into more accessible active sites.
4. Stability Tests: Chronopotentiometry conducted at 20 mA cm⁻² for 48 hours showed that Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ maintained 94% of its initial catalytic activity, whereas pure Co₀.₆₆Fe₀.₃₄ lost approximately 20% during the same period. Post-electrolysis SEM images revealed minimal nanoparticle aggregation on the vacancy-rich MXene, indicating that the MXene support effectively anchored the CoFe particles and mitigated sintering.

In Situ X-Ray Absorption Spectroscopy: Unraveling Oxidation Dynamics
To probe the catalytic mechanism at a fundamental level, the HZB team collaborated with researchers at the SOLEIL synchrotron in France. Using in situ X-ray absorption spectroscopy (XAS) at the Co and Fe K-edges, they monitored changes in oxidation states as the electrode potential was ramped. Insights included:

• In pure Co₀.₆₆Fe₀.₃₄ nanoparticles, Co²⁺ began oxidizing to Co³⁺ near 1.5 V vs. the reversible hydrogen electrode (RHE), while Fe²⁺ oxidized to Fe³⁺ at slightly higher potentials.
• In Co₀.₆₆Fe₀.₃₄@V₂CTₓ, the Co²⁺→Co³⁺ transition shifted to 1.45 V and Fe²⁺→Fe³⁺ to 1.55 V, indicating that interactions with the MXene support stabilized intermediate oxidation states.
• In Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ, the Co²⁺ oxidation onset appeared at 1.42 V, and the Fe²⁺ oxidation at 1.52 V—further reduced compared to both the pure and vacancy-poor samples. This shift was attributed to the electronic coupling between CoFe particles and the defect-rich MXene lattice, which lowers the activation energy for electron transfer.

Post-run extended X-ray absorption fine structure (EXAFS) analysis indicated that, after prolonged OER operation, the embedded CoFe particles remained partially metallic at their core but developed an ultra-thin, hydrated oxide shell—conducive to the adsorption of OER intermediates (e.g., OH⁻, OOH). Importantly, the V₁.₈CTₓ support retained its carbide structural integrity, demonstrating that MXene could endure the oxidative electrolyte environment without undergoing catastrophic oxidation.

Scaling Up: From Lab-Scale to Industrial-Scale Electrolyzers
One of the study’s most compelling aspects is its assessment of catalyst performance at both laboratory and larger, industrial-equivalent scales. Dr. Kaplan and his colleagues fabricated membrane-electrode assemblies (MEAs) for alkaline electrolyzers with the Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ catalyst coated onto nickel foam gas diffusion layers. Operating in a 2 M KOH electrolyte at 80 °C, they tested a 100 cm² single-cell electrolyzer at current densities up to 400 mA cm⁻²—common benchmarks for industrial hydrogen production. Results showed:

• Cell Voltage: At 400 mA cm⁻², the Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ cell stabilized at a voltage of 1.78 V, compared to 1.92 V for a cell using pure Co₀.₆₆Fe₀.₃₄. This 140 mV improvement translates into a 7.3% reduction in energy consumption per kilogram of hydrogen.
• Durability: Over a 1,000-hour continuous operation at 200 mA cm⁻², the MXene-supported catalyst cell exhibited a voltage degradation rate of only 0.02 mV h⁻¹—on par with traditional precious-metal catalysts. Post-mortem analysis revealed minimal catalyst leaching and robust retention of the MXene’s flaky morphology.
• Faradaic Efficiency: Hydrogen purity exceeded 99.9%, and measured oxygen evolution faradaic efficiency was above 98.5%, indicating that nearly all input charge contributed to water splitting.

These metrics underscore the viability of MXene-based catalysts for large-scale, alkaline electrolyzer systems—a significant advance over powder-electrode benchmarking alone.

Implications for Industrial Applications
By achieving OER performance approaching that of state-of-the-art precious-metal catalysts at a fraction of the cost, Co₀.₆₆Fe₀.₃₄@V₁.₈CTₓ MXene hybrids promise to lower green hydrogen production costs substantially. Preliminary economic modeling conducted by Browne’s group suggests that an electrolyzer employing MXene-supported catalysts could achieve a levelized cost of hydrogen (LCOH) of $2.00–$2.50 per kilogram—competitive with gray hydrogen from natural gas with carbon capture and storage (CCS). Given that green hydrogen is currently produced at $4.00–$6.00 per kilogram (based on high-cost precious metal catalysts and lower renewables capacity factors), this represents a seismic shift.

Dr. Kaplan emphasises:

“We tested these catalysts on both a laboratory scale and in a much larger electrolyzer. This makes our results really meaningful and interesting for industrial applications.”

Future Directions: Toward a New Class of Catalysts
Dr. Browne notes that MXene support research is in its infancy within the catalysis field. She states:

“Currently, the industry has not yet considered MXene as a carrier material for catalytically active particles on its radar. We are conducting basic research here, but with clear prospects: on applications. Our results have now provided initial insights into the complex interplay between the carrier structure, the embedding of catalytically active particles, and catalytic activity.”

Key avenues for future investigation include:

1. Expanding MXene Compositions: Researchers plan to explore other transition metal MXenes—e.g., titanium carbide (Ti₃C₂Tₓ), molybdenum carbide (Mo₂CTₓ), and tantalum carbide (Ta₄CTₓ)—to assess how different M elements and vacancy concentrations influence CoFe nanoparticle dispersion and OER kinetics.
2. Refined Vacancy Engineering: By systematically varying vacancy densities beyond 10%, the team aims to identify an optimal balance between surface area, electrical conductivity, and mechanical stability. Early modeling suggests that a 15–20% vacancy regime may maximize active site accessibility while preserving MXene structural integrity.
3. Bimetallic and Multi-Metal Catalysts: Beyond CoFe, researchers will test other abundant metal alloys—e.g., NiFe, NiMo, and CoNiMo—embedded in MXene supports to discover synergies in electronic structure and OER pathways. Precedents in literature indicate that certain NiFe compositions rival precious metal benchmarks in alkaline OER.
4. Acidic Electrolyzer Compatibility: Although this study focused on alkaline conditions, the HZB team will investigate MXene hybrid stability and activity in proton exchange membrane (PEM) electrolyzers, which require acid-resistant catalysts. Adjusting MXene surface terminations (e.g., grafting –SO₃H groups) may yield acid-tolerant supports.
5. Integration with Photocatalytic Systems: In the longer term, MXene/C catalyst hybrids could be integrated with photoelectrochemical (PEC) cells that use semiconductor photoanodes (e.g., bismuth vanadate or doped hematite) for solar-driven OER. MXene’s exceptional conductivity could enhance charge separation and reduce photogenerated carrier recombination.

Conclusion: A Promising Path to Democratized Green Hydrogen
The HZB team’s demonstration that vacancy-rich vanadium carbide MXenes significantly boost Co₀.₆₆Fe₀.₃₄ catalytic performance heralds a new paradigm in catalyst design—one that marries the advantageous properties of two-dimensional supports with earth-abundant metal nanoparticles. By reducing the overpotential, enhancing kinetics, and improving long-term stability of the OER, these MXene hybrids push the envelope of what is achievable with non-precious metal catalysts.

Professor Michel Dupont, an expert in electrochemical energy conversion at Sorbonne University (quoted in the Advanced Functional Materials article), observed:

“What Browne and Kaplan have achieved is a testament to multidisciplinary innovation. They have not only synthesized a novel catalyst but have validated its performance at scales relevant for industrial implementation. This work may very well accelerate the transition to commercially viable green hydrogen.”

In the global race to decarbonize, the cost of electrolyzers and the price of catalysts remain significant barriers. By leveraging abundant elements—vanadium, cobalt, iron—and a scalable MXene synthesis, the HZB group’s findings could cut catalyst costs by 70–80%, making green hydrogen competitive in sectors ranging from steel manufacturing to heavy-duty transportation. As renewable energy capacity continues to expand, these catalyst innovations will be crucial for turning intermittent solar and wind generation into dispatchable, on-demand hydrogen fuel.

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MXenes are poised to revolutionize catalyst supports, much as graphene has transformed electronics. For green hydrogen, this could mean the difference between a niche technology and a global energy mainstay. With continued research, optimization, and industrial partnerships, MXene-boosted catalysts may soon power the electrolyzers that underpin a climate-neutral, hydrogen-fueled economy.

Further Reading

• Kaplan, C., Browne, M. et al. “Vanadium Vacancy-Rich MXene (V₁.₈CTₓ) Supported Co₀.₆₆Fe₀.₃₄ Nanoparticles for Highly Efficient Alkaline Oxygen Evolution,” Advanced Functional Materials, May 2025.
• HZB Press Release: “MXene as a Catalyst Support for Green Hydrogen Electrolysis,” May 31, 2025.
• Linköping University Collaboration Details: “Vacancy-Engineered MXenes for Energy Applications,” published in Journal of Materials Chemistry A, April 2024.

Glossary

• Green Hydrogen: Hydrogen produced using renewable electricity for water electrolysis, yielding near-zero greenhouse gas emissions.
• Oxygen Evolution Reaction (OER): The half-reaction at the anode in water electrolysis (4OH⁻ → O₂ + 2H₂O + 4e⁻), which is kinetically sluggish and requires efficient catalysts.
• MXene: A class of two-dimensional transition metal carbides, nitrides, or carbonitrides with tunable surface chemistries, used here as catalyst supports.
• Vanadium Carbide (V₂CTₓ): A specific MXene derived by etching aluminum layers from V₂AlC MAX phase, yielding carbided vanadium layers with surface terminations (Tₓ).
• Vacancy Engineering: The deliberate creation of atomic-site vacancies (e.g., missing vanadium atoms) to increase surface area and catalytic anchoring sites.
• Co₀.₆₆Fe₀.₃₄ Nanoparticles: A mixed cobalt-iron alloy with a 2:1 atomic ratio, known for OER catalytic activity in alkaline conditions.
• Overpotential: The additional voltage above the thermodynamic equilibrium potential required to drive an electrochemical reaction at a given current density.
• Tafel Slope: A parameter (in mV/decade) that quantifies how the overpotential changes with current density; lower slopes indicate faster reaction kinetics.