Key Takeaways & Executive Findings
- •• • FeY-Pt-C (20% Pt) delivers 1071 mA mg_Pt^-1 mass activity, 2.23× that of Pt-C (20% Pt), directly reducing Pt loading and catalyst cost for electrochemical hydrogen pumps. • • Under 5000 ppm NH3, FeY-Pt-C retains 93.1% of initial activity, whereas conventional Pt-C suffers severe poisoning; this threshold exceeds typical residual ammonia levels in ammonia-cracked hydrogen, enabling direct purification without upstream scrubbing. • • Machine learning with Shapley Additive Explanations identified Fe and Y as optimal dual modulators, cutting experimental screening from exhaustive trial-and-error to a targeted alloy design, accelerating catalyst development cycles. • • Fe specifically promotes PtY alloy formation over stable Y oxide phases, ensuring electronic modulation of Pt that weakens NH3 adsorption; without Fe, Y oxide formation renders the catalyst ineffective, highlighting a critical compositional constraint for scalable synthesis.
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Abstract
Trace ammonia in hydrogen derived from ammonia cracking poisons proton exchange membrane fuel cell anodes, degrading performance and durability. Conventional separation technologies such as pressure swing adsorption suffer from high equipment costs, large system volume, and low durability. This study employs machine learning coupled with Shapley Additive Explanations to identify Fe and Y as dual transition-metal modulators that enhance ammonia tolerance in Pt-based hydrogen oxidation reaction (HOR) catalysts. Fe facilitates PtY alloy formation, suppressing stable Y oxide phases and modulating Pt electronic properties. The resulting FeY-Pt-C (20% Pt) catalyst achieves a mass activity of 1071 mA mg_Pt^-1, 2.23-fold higher than Pt-C (20% Pt). Under 5000 ppm NH3, FeY-Pt-C retains 93.1% of its initial electrocatalytic activity, demonstrating exceptional ammonia poisoning resistance. This dual-metal regulation strategy offers a viable route for electrochemical hydrogen pumps to purify hydrogen from ammonia cracking, addressing a critical bottleneck in ammonia-mediated hydrogen transport.
1. Introduction
Hydrogen storage and transport face inherent penalties: cryogenic or high-pressure containment, leakage, and embrittlement. Ammonia, with 17.6 wt% gravimetric hydrogen capacity, offers a lower-cost, COx-free vector, but residual NH3 at trace levels poisons the anode catalyst in proton exchange membrane fuel cells, slashing activity and durability. Pressure swing adsorption, chemical fractionation, and adsorptive separation are operationally simple but incur high equipment costs, large footprints, and poor durability; cyclic pressure swings further prolong purification. Electrochemical hydrogen pumps (EHPs) promise compact, efficient separation, yet their Pt-based HOR catalysts remain vulnerable to ammonia.
This study deploys machine learning and Shapley Additive Explanations to screen transition metals for ammonia tolerance, identifying Fe and Y as dual regulators. Fe drives PtY alloy formation, preventing stable Y oxide phases and tuning Pt electronic structure to weaken NH3 adsorption while enhancing HOR activity. The FeY-Pt-C (20% Pt) catalyst achieves 1071 mA mg_Pt^-1 mass activity—2.23-fold above Pt-C—and retains 93.1% activity under 5000 ppm NH3. This co-regulation strategy directly addresses the ammonia poisoning bottleneck, enabling EHPs to purify hydrogen from ammonia cracking without upstream scrubbing.
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ZHAO Yanshen, WANG Xiaoqing, WANG Rui, WU Fanglin, DUAN Wenjing, LI Hao, TANG Haolin (2025). Ammonia-Resistant Pt-Based HOR Catalyst with Fe/Y Co-Regulation for High-Efficiency Hydrogen Purification Enabled by Machine Learning. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3399-3
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Frequently Asked Questions
What is the specific failure mechanism of conventional Pt catalysts under ammonia exposure, and how does FeY-Pt-C mitigate it?
Conventional Pt catalysts suffer strong NH3 adsorption on Pt sites, blocking hydrogen access and reducing HOR activity. FeY-Pt-C modulates Pt electronic properties via PtY alloy formation, weakening NH3 binding. Under 5000 ppm NH3, FeY-Pt-C retains 93.1% of initial activity, whereas Pt-C undergoes severe poisoning, demonstrating that electronic modulation directly suppresses the poisoning pathway.
How does the mass activity of FeY-Pt-C compare to commercial Pt-C, and what is the industrial implication for Pt loading?
FeY-Pt-C (20% Pt) achieves 1071 mA mg_Pt^-1, 2.23-fold higher than Pt-C (20% Pt). This allows equivalent HOR performance with less than half the Pt loading, directly reducing catalyst cost—a critical factor for scaling electrochemical hydrogen pumps, where Pt constitutes a major capital expense.
What is the role of Fe in stabilizing the PtY alloy, and what happens if Fe is omitted?
Fe facilitates PtY alloy formation by suppressing the stable oxide phase of Y. Without Fe, Y tends to form oxides that do not modulate Pt electronic properties, resulting in poor ammonia tolerance and lower HOR activity. The Fe/Y synergy is therefore essential for achieving the observed 93.1% activity retention under 5000 ppm NH3.
Can this catalyst tolerate ammonia concentrations beyond 5000 ppm, and what are the operational limits?
The study reports 93.1% activity retention at 5000 ppm NH3, which exceeds typical residual ammonia levels in ammonia-cracked hydrogen (often <1000 ppm). Higher concentrations may accelerate poisoning, but the electronic modulation provides a margin. Long-term durability tests under cyclic ammonia exposure are needed to establish upper thresholds for industrial EHP operation.
What scalability challenges exist for synthesizing FeY-Pt-C, and how does machine learning accelerate optimization?
Scalability requires uniform Fe and Y incorporation and prevention of Y oxide phases during synthesis. Machine learning with Shapley Additive Explanations identified Fe and Y from a broad compositional space, reducing experimental iterations. The 20% Pt loading is compatible with conventional impregnation or colloidal methods, but continuous-flow synthesis must control alloy phase purity to maintain the 2.23-fold activity advantage.
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