Entropy-Driven Direct Air Electrofixation.

According to the principles of chemical thermodynamics, the catalytic activation of small molecules (like N in air and CO in flue gas) generally exhibits a negative activity dependence on O owning to the competitive oxygen reduction reaction (ORR). Nevertheless, some catalysts can show positive activity dependence for N electrofixation, an important route to produce ammonia under ambient condition. Here we report that the positive activity dependence on O of (NiCoFeMnMo)S catalyst arises from high-entropy mechanism. Through experimental and theoretical studies, we demonstrate that under the reaction condition in the mixed N/O, the adsorption of O on high-entropy catalyst contributes to activating N 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, the system for direct air electrofixation has demonstrated an ammonia yield rate of 47.70 μg h cm, which is even 1.5 times of pure N feedstock (31.92 μg h cm), 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.