(710d) High-Performance Electrocatalytic Nitrate Reduction to Ammonia on Ordered Intermetallic Cupd Nanocubes: Breaking Adsorption-Energy Scaling Limitations

The electrochemical nitrate reduction reaction (NO₃RR) to ammonia is an essential step toward restoring the globally disrupted nitrogen cycle. With interpretable machine learning (ML), we unravel a mechanism of breaking adsorption-energy scaling relations through the site-specific Pauli repulsion interactions of the metal d-states with adsorbate frontier orbitals. The non-scaling behavior can be realized on (100)-type sites of ordered B2 intermetallics, in which the orbital overlap between the hollow *N and subsurface metal atoms is significant while the bridge-bidentate *NO₃ is not affected. Among a few promising systems suggested by interpretable ML and DFT calculations, we successfully synthesized the ordered intermetallic B2 CuPd nanocubes terminated with (100) facets using a one-pot solution-phase method. The CuPd catalyst exhibits superior NO₃RR performance compared with Cu and Pd nanocubes in alkaline media, validating theoretical predictions. Specifically, these CuPd nanocubes demonstrated exceedingly high catalytic performance of NO₃RR toward NH₃ with a Faradaic efficiency (FE) of 92.5% at -0.5 V vs. reversible hydrogen electrode (RHE) and a yield rate of 6.25 mmol h^-1 g^-1 at -0.6 V vs. RHE. Furthermore, these B2 CuPd nanocubes demonstrated high stability over 12 h electrolysis operation in the electrolyte of 1 M KNO₃ and 1 M KOH, which is highly desirable for practical applications. Bayeschem models suggest that while the d-band center of Cu sites at CuPd nanocubes shifts up in energy that favors the bridge-bidentate *NO₃ adsorption, the hollow *N is destabilized due to a dominant role of Pauli repulsion from the subsurface Pd d-orbitals, facilitating the protonation of N-bonded species toward NH₃. This study demonstrates the concept of combining interpretable ML with precision synthesis for the design of new catalytic systems that break adsorption-energy scaling relations and the corresponding limitations on attainable catalytic performance.