Hydrogen Evolution Catalysis
Field
Electrocatalysis, Clean Energy
Reaction
2H+ + 2e- → H2
Best Catalyst
Platinum (benchmark)
Goal
Earth-abundant alternatives
Capstone Papers
3,046 (250+ citations)
Hydrogen evolution reaction (HER) catalysis is central to green hydrogen production via water electrolysis. While platinum group metals (PGMs) are highly active, their scarcity and cost drive research into earth-abundant alternatives including transition metal compounds, carbon-based materials, and single-atom catalysts.
This research survey covers highly-cited papers on HER mechanism, catalyst design, and performance benchmarking.
Reaction mechanism
HER proceeds via two main pathways depending on hydrogen adsorption free energy (ΔGH):
Volmer step: H+ + e- → H*
Heyrovsky step: H* + H+ + e- → H2
Tafel step: H* + H* → H2
* denotes adsorbed species
- Volmer-Heyrovsky: Proton directly combines with adsorbed hydrogen. Favored at low coverage.
- Volmer-Tafel: Two adsorbed hydrogens combine. Favored on Pt surfaces with optimal ΔGH ≈ 0.
- Tafel slope: ~30 mV/dec (Tafel-limited), ~40 mV/dec (Heyrovsky), ~120 mV/dec (Volmer-limited)
Design principle: The Sabatier principle dictates ΔGH ≈ 0 for optimal activity. Too strong adsorption inhibits H2 release; too weak limits H* formation.
Noble metal catalysts
Platinum remains the benchmark for HER but cost limits large-scale deployment:
- Pt/C: Near-zero overpotential, 0.5-1 mg/cm2 loading in commercial electrolyzers
- Pt alloys: Pt-Ni, Pt-Co reduce Pt loading while maintaining activity
- Pt nanostructures: Nanowires, nanoframes maximize surface area and mass activity
- Ultra-low loading: Atomic layer deposition achieves <10 μg/cm2 with comparable performance
| Catalyst |
η10 (mV) |
Tafel (mV/dec) |
Stability |
| Pt/C (20%) |
~25 |
30 |
Excellent |
| Pt-Ni alloy |
~30 |
35 |
Good (Ni leaching) |
| Pt nanowires |
~20 |
28 |
Excellent |
Transition metal dichalcogenides
MoS2 and related TMDs have emerged as promising non-precious HER catalysts:
- Edge sites: DFT calculations show MoS2 edges have ΔGH ≈ 0.08 eV, close to optimal. Basal planes are inactive.
- 1T phase: Metallic polymorph has higher conductivity and more active sites than 2H-MoS2
- Defect engineering: S vacancies create additional active sites with near-optimal ΔGH
- Heteroatom doping: Co, Fe, Ni doping improves activity and conductivity
State-of-the-art: Strained 1T-MoS2 nanosheets achieve η10 < 100 mV with 1000+ hour stability.
Metal phosphides and carbides
Transition metal phosphides (TMPs) and carbides show near-Pt activity:
- Ni2P: η10 ≈ 60 mV, ensemble effect with P atoms modulating Ni electronic structure
- CoP: η10 ≈ 55 mV on nanostructured forms, stable in acid and base
- FeP: Lower cost, η10 ≈ 70 mV with good stability
- Mo2C: Carbide analogue with Pt-like d-band structure, η10 ≈ 80 mV
Phosphidation of metal foams or MOF-derived structures creates high-surface-area electrodes with excellent mass transport.
Single-atom catalysts
Single-atom catalysts (SACs) maximize metal utilization and enable unique reaction pathways:
- Pt1/carbon: 37x mass activity improvement over Pt nanoparticles
- Ni-N-C: Non-precious SAC with η10 ≈ 100 mV in acid
- Co-N-C: MOF-derived, comparable to Pt in alkaline media
- Dual-atom: Fe-Co pairs show synergistic effects and improved stability
Synthesis routes: High-temperature pyrolysis of metal-doped MOFs or polymers, atomic layer deposition on carbon supports.
Key papers
See also