Disorder-Tuned B5 Ensembles for Ammonia Decomposition on Co–Cu–Fe–Mo–Ni High-Entropy Alloys

We establish an end-to-end framework that generalizes across alloy families and, applied here to Co–Cu–Fe–Mo–Ni, it maps alloy composition to B5 step ensembles on fcc(211), *N-adsorption energies ΔE(*N), and rate for ammonia decomposition reaction (ADR). The workflow—DFT-trained cluster expansions (CE) → Metropolis Monte Carlo (MMC) → microkinetics—predicts site-resolved ΔE(*N) and enables composition-wide maps of site-specific turnover frequency (TOF) and surface-averaged activity (⟨TOF⟩). MMC captures temperature-driven Cu enrichment at the outermost layer, shifting ΔE(*N) toward weaker binding relative to statistically random surfaces and suppresses ⟨TOF⟩. Lowering Cu systematically increases activity; by contrast, Cu-free Co–Fe–Mo–Ni medium-entropy alloys (MEAs) cluster near the volcano maximum and deliver high, composition-robust rates. Site-level analysis shows that the most active B5 ensembles are Cu-lean and typically multimetallic, consistent with surface-averaged trends. DFT validation on 40 CE-screened high-activity B5 sites confirms predictive fidelity. The framework yields practical, testable design rules—minimize Cu participation at B5 and preserve configurational disorder (e.g., thermal-shock)—and is readily extensible to other alloy families and to both thermochemical and electrochemical reactions.