Breaking linear scaling relations by strain engineering on MXene for boosting N2 electroreduction

The development of N2 reduction reaction (NRR) electrocatalysts with excellent activity and selectivity is of great significance, but adsorption-energy linear scaling relations between reaction intermediates severely hamper the realization of this aspiration. Here, we propose an elegant strain engineering strategy to break the linear relations in NRR to promote catalytic activity and selectivity. Our results show that the N-N bond lengths of adsorbed N2 with side-on and end-on configurations exhibit opposite variations under strains, which is illuminated by establishing two different N2 activation mechanisms of "P-P" (Pull-Pull) and "E-E" (Electron-Electron). Then, we highlight that strain engineering can break the linear scaling relations in NRR, selectively optimizing the adsorption of key NH2NH2** and NH2* intermediates to realize a lower limiting potential (UL). Particularly, the catalytic activity-selectivity trade-off of NRR on MXene can be circumvented, resulting in a low UL of -0.25 V and high Faraday efficiency (FE), which is further elucidated to originate from the strain-modulated electronic structures. Last but not least, the catalytic sustainability of MXene under strain has been guaranteed. This work not only provides fundamental insights into the strain effect on catalysis but also pioneers a new avenue toward the rational design of superior NRR catalysts.

Boosting charge-transfer in tuned Au nanoparticles on defect-rich TiO2 nanosheets for enhancing nitrogen electroreduction to ammonia production

The electrocatalytic nitrogen reduction reaction (eNRR) to ammonia (NH₃) has been recognized as an effective, carbon-neutral, and great-potential strategy for ammonia production. However, the conversion efficiency and selectivity of eNRR still face significant challenges due to the slow transfer kinetics and lack of effective N₂ adsorption and activation sites in this process. Herein, we designed and fabricated defect-rich TiO₂ nanosheets furnished with oxygen vacancies (OVs) and Au nanoparticles (Au/TiO_2-x) as the electrocatalyst for efficient N₂-fixing. The experimental results demonstrate that OVs act as active sites, which enable efficient chemisorption and activation of N₂ molecules. The Au nanoparticles loaded on the OVs-rich TiO₂ nanosheets not only accelerate charge transfer but also change the local electronic structure, thus enhancing N₂ adsorption and activation. In this work, the optimal Au/TiO_2-x electrocatalyst displays a considerable NH₃ yield activity of 12.5 μg h^-1 mg_cat.^-1 and a faradaic efficiency (FE) of 10.2 % at -0.40 V vs reversible hydrogen electrode (RHE). More importantly, the Au/TiO_2-x exhibits a stable N₂-fixing activity in cycling and it persists even after 80 h of consecutive electrolysis. Density functional theory (DFT) calculations reveal that the OVs serve as the active sites in TiO₂, while Au nanoparticles are crucial for improving N₂ chemisorption and lowering the reaction energy barrier by facilitating the charge transfer for eNRR with a distal hydrogenation pathway. This research offers a rational catalytic site design for modulating charge transfer of active sites on metal-supported defective catalysts to boost N₂ electroreduction to NH₃.