Metastable Phase Noble-Metal-Free Core-Shell Structure for Efficient Electrocatalytic Nitrobenzene Transfer Hydrogenation.

In order to study the catalytic behavior of a metastable-phase catalyst in electrocatalytic hydrogenation, we report a new metastable-phase noble-metal-free core-shell catalyst with a metastable hexagonal closest packed (hcp) phase Ni as the shell and face-centered-cubic (fcc) phase Cu as the core (Cu@hcp Ni NPs) for electrocatalytic hydrogenation of nitrobenzene (Ph-NO₂) to aniline (Ph-NH₂). Using H₂O as the hydrogen source, it achieves up to 99.63% Ph-NO₂ conversion and ∼100% Ph-NH₂ selectivity, with an improved activity turnover frequency (TOF: 6640 h^-1), much higher than those of hcp Ni NPs (5183.7 h^-1) and commercial Pt/C (3537.6 h^-1). It can also deliver a variety of aminoarenes with outstanding selectivity and excellent functional group compatibility with several groups. Mechanistic studies have shown that the introduction of Cu enhances hcp Ni's ability to dissociate water in situ to produce H* and improves the hydrogenation rate, resulting in the rapid conversion of Ph-NO₂ to the final product Ph-NH₂.