Metallene, a group of graphene-like two-dimensional (2D) nanomaterials with a thickness less than 5 nm 36, 37.

Furthermore, the electrocatalytic activity of SAAs catalysts can be further improved by the precise regulation for morphology and structure 34, 35. Thus, the electron effect and metal-support interaction of SAAs can promote effective dissociation of reactants and optimize the adsorption/desorption of key intermediates to achieve an optimum balance between reactants and intermediates, leading to high activity and selectivity 32, 33. For example, Duan and co-workers designed a Ru 1Cu SAAs with isolated Ru atoms on Cu nanowires for the electrocatalytic conversion of 5-hydroxymethylfurfural (HMF) to 2,5-dihydroxymethylfuran (DHMF), where the introduction of Ru single-atom sites facilitates the dissociation of H 2O to produce H* species for the HMF hydrogenation process 31. Recently, the single-atom alloys (SAAs) catalysts, consisting of exogenous isolated metal atoms dispersed on the surface of the metal host 23, 24, as a promising material with the advantages of high active atom utilization of single-atom catalysts (SACs) and alloy synergistic effect 25, 26, have been in the field of various electrocatalytic energy conversions 27, 28, 29, 30. To address these bottlenecks, it is fundamental to explore efficient bifunctional electrocatalysts for activating reaction pathways of the directed synthesis towards Ph-NH 2 and formate. Nevertheless, both Ph-NO 2-to-Ph-NH 2 and methanol-to-formate are multi-step reaction processes and are limited by numerous side reactions 21, 22. In view of this, the construction of Ph-NO 2 ERR-MOR coupled electrolytic system is a promising strategy for achieving high-value chemical synthesis from sustainable organic electrocatalytic conversion. Currently, the cheap and widespread methanol (CH 3OH, 350 USD/t) is considered an appropriate precursor for the high-value formate (HCOO −, 1300 USD/t) synthesis via anodic electrooxidation reaction 17, 18, and methanol electrooxidation reaction (MOR) coupled with various electrocatalytic reactions has attracted widespread research interest worldwide 19, 20. In contrast, the anodic biomass electrooxidation reaction not only can achieve the upgrading of cheap biomass but also offers the advantages of low energy consumption and high electrolysis efficiency 14, 15, 16. Notably, the anodic reaction for the conventional cathodic Ph-NO 2 electroreduction reaction (Ph-NO 2 ERR) is a sluggish kinetic oxygen evolution reaction (OER) 12, 13. Among the numerous organic electrocatalytic conversion reactions, the cathodic nitrobenzene (Ph-NO 2) electroreduction for aniline (Ph-NH 2) synthesis is regarded as a more low-carbon and environment-friendly green Ph-NH 2 synthesis process using H 2O and electrons as the hydrogen source and reductant, compared with high pollution and harsh conditions of traditional chemical synthesis method 8, 9, 10, 11. The organic electrocatalytic conversion, driven by electricity generated from renewable energy sources at ambient temperature and pressure 3, 4, is a green synthesis route for achieving controlled conversion of low-cost organic compounds into high-value chemicals and holds considerable research significance and application potential in the chemical industry and organic synthesis 5, 6, 7. The utilization of renewable energy is a crucial pathway for solving the increasing energy crisis and promoting the green low-carbon transformation of energy 1, 2. The synergistic catalytic effect and H*-spillover effect can improve catalytic reaction process and reduce energy barrier for reaction process, thus enhancing electrocatalytic reaction activity and target product selectivity.

Density functional theory calculations reveal the electron effect between Cu single-atom and Rh host and catalytic reaction mechanism. In the coupled electrocatalytic system, the Cu single-atom-Rh metallene arrays on Cu foam requires only the low voltages of 1.18 V to reach current densities of 100 mA cm −2 for generating aniline and formate, with up to ~100% of nitrobenzene conversion/ aniline selectivity and over ~90% of formate Faraday efficiency, achieving synthesis of high-value chemicals. Here, we report a Cu single-atom dispersed Rh metallene arrays on Cu foam for cathodic nitrobenzene electroreduction reaction and anodic methanol oxidation reaction. Organic electrocatalytic conversion is an essential pathway for the green conversion of low-cost organic compounds to high-value chemicals, which urgently demands the development of efficient electrocatalysts.

Cathode reaction example