Asymmetric acidic/alkaline N2 electrofixation accelerated by high-entropy metal–organic framework derivatives

Abstract

High-entropy materials are composed of five or more metal elements with equimolar or near-equimolar concentrations within one crystal structure, which offer remarkable structural properties for many applications. Despite previously reported entropy-driven stabilization mechanisms, many high-entropy materials still tend to decompose to produce a variety of derivatives under operating conditions. In this study, we use transition-metal (Ni, Co, Ni, Zn, V)-based high-entropy metal–organic frameworks (HE-MOFs) as the precursors to produce different derivatives under acidic/alkaline treatment. We have shown that HE-MOFs and derivatives have shown favorable kinetics for N2 electrofixation in different pH electrolytes, specifically cathodic nitrogen reduction reaction in acidic media and anodic oxygen evolution reaction in alkaline media. To buffer the pH mismatch, we have further constructed an asymmetric acidic/alkaline device prototype by using bipolar membranes. As expected, the prototype showed remarkable activities, with an NH3 yield rate of 42.76 μg h−1 mg−1, and Faradaic efficiency of 14.75% and energy efficiency of 2.59%, which are 14.4 and 4.4 times larger than those of its symmetric acidic and alkaline counterparts, respectively.