(710d) High-Performance Electrocatalytic Nitrate Reduction to Ammonia on Ordered Intermetallic Cupd Nanocubes: Breaking Adsorption-Energy Scaling Limitations
AIChE Annual Meeting
Friday, November 18, 2022 - 1:06pm to 1:24pm
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.