Entropy-Driven Direct Air Electrofixation.

According to the principles of chemical thermodynamics, the catalytic activation of small molecules (like N 2 in air and CO 2 in flue gas) generally exhibits a negative activity dependence on O 2 owning to the competitive oxygen reduction reaction (ORR). Nevertheless, some catalysts can show positive activity dependence for N 2 electrofixation, an important route to produce ammonia under ambient condition. Here we report that the positive activity dependence on O 2 of (Ni 0.20 Co 0.20 Fe 0.20 Mn 0.19 Mo 0.21 ) 3 S 4 catalyst arises from high-entropy mechanism. Through experimental and theoretical studies, we demonstrate that under the reaction condition in the mixed N 2 /O 2 , the adsorption of O 2 on high-entropy catalyst contributes to activating N 2 molecules characteristic of elongated N≡N bond lengths. As comparison to the low- and medium-entropy counterparts, high entropy can play the second role of attenuating competitive ORR by displaying a negative exponential entropy-ORR activity relationship. Accordingly, benefiting from the O 2 , the system for direct air electrofixation has demonstrated an ammonia yield rate of 47.70 μg h -1  cm -2 , which is even 1.5 times of pure N 2 feedstock (31.92 μg h -1  cm -2 ), overtaking all previous reports for this reaction. We expect the present finding providing an additional dimension to high entropy that leverages systems beyond the constraint of traditional rules.