Rational design of precious tetrametallic single-cluster catalysts for electrocatalytic nitrate reduction reaction

Single cluster catalysts (SCCs) with high metal loading can exhibit extraordinary catalytic activity in electrocatalytic reactions, but the rational design of active sites remains a challenge. Herein, we proposed a series of SCCs with pyramid-shaped precious tetrametallic clusters anchored on g-CN monolayer (M₄/g-CN) as efficient catalysts for the electrochemical reduction of nitrate to ammonia (NO₃RR). By means of first-principle computations, the stability, catalytic mechanism and activity, as well as selectivity of these SCCs are systematically investigated. The calculation results show that most SCCs (Ru₄/g-CN, Rh₄/g-CN, Pd₄/g-CN, Os₄/g-CN, Ir₄/g-CN, Pt₄/g-CN) are thermodynamically stable due to the strong binding energy and significant charge transfer behavior between tetrametallic clusters and g-CN support. More important, the volcano curve between limiting potentials and adsorption free energy of NO₃^‾ can be established, in which Ir₄/g-CN can exhibit optimal NO₃RR activity due to its location of volcano top. Further analysis of electronic structures reveals that the special pyramid configuration can significantly promote the enrichment of charge on active site and elevate its d-band center, and thus facilitates the NO₃RR. This finding pours new vigor into the development of the SCCs family.