Active Diatomic Pairs Induced Interlayer Spacing Engineering in 2D Materials for Highly Efficient Energy Conversion Device

Abstract

Ammonia, the second largest commercialized synthetic chemical in the world, is widely used for fertilizer and all nitrogen-atom-containing chemicals production. Energy conversion devices by electrochemical nitrate reduction reaction (eNO3RR) offer a green and appealing approach for sustainable ammonia synthesis but hindering by the multi-step chemical reaction and competitive hydrogen generation. To this end, exploring efficient nitrate-to-ammonia conversion devices play a critical role in developing ammonia electrosynthesis. Two-dimensional (2D) materials, like MoS2 and SnS2, have been considered promising energy electrocatalytic materials owing to the advantages of large specific areas that not only provide much more active sites but act as appropriate support to combine other materials. Recently, interlayer engineering on 2D materials has attracted intense interest from scientists because it could tune the chemical affinity of absorbates, which determines the energy barriers during multi-step electrocatalysis device. Therefore, it is valuable to investigate the effect of interlayer spacing in 2D materials on eNO3RR. Active diatomic A-B pairs, such as diatomic Pt-Ce and Pd-Ce pairs, have strong interactions that can be introduced into 2D materials to trigger the interlayer spacing change. For example, the lanthanide series rare earth element (Ce) can be a potential candidate to achieve interlayer expansion since it has a relatively higher atomic radius than most of the atoms, while intercalating Pt or Pd can close the interlayer spacing through solid interaction. In this work, by introducing active diatomic Pt-Ce and Pd-Ce pairs into SnS nanosheets through doping and intercalating, the interlayer spacing of 2D SnS nanosheets achieves both expansion (~6.5 %) and compression (~8.0%). More importantly, the samples with various interlayer spacing show distinguishing nitrate reduction efficiency. The SnS nanosheet with compressed interlayer spacing can reach high ammonia Faradaic efficiencies (surpassing 90%) and yield rate (~0.31 mmol cm− 2 h− 1). Different characterize tools are applied to investigate the mechanism, including in-situ Raman spectra and DFT calculations. The results attribute to the variational delocalized electron density of localized p-orbital in Sn, which contribute to the faster conversion of the rate-determining step (*NO3→*NO2) and the higher chemical affinity of NO3 - and NO2 - in eNO3RR, and the suppressed hydrogen evolution reaction in the meantime. Taken together, our work verifies the feasibility of tailoring the interlayer spacing of 2D materials by active diatomic pairs and further implicates interlayer engineering in promoting efficient electrochemical nitrate conversion devices.