Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Tuning Electron Distribution of Single‐Atomic Iron Sites

Abstract

Electrocatalytic nitrogen reduction reaction (NRR) playsavital role for next-generation electrochemical energy conversion technologies.H owever,t he NRR kinetics is still limited by the sluggish hydrogenation process on noble-metalfree electrocatalyst. Herein, we report the rational design and synthesis of ah ybrid catalyst with atomic iron sites anchored on aN ,O-doped porous carbon (Fe SA-NO-C) matrix of an inverse opal structure,leading to aremarkably high NH 3 yield rate of 31.9 mg NH 3 h À1 mg À1 cat. and Faradaic efficiency of 11.8 % at À0.4 Vf or NRR electrocatalysis,o utperformed almost all previously reported atomically dispersed metal-nitrogen-carbon catalysts.T heoretical calculations revealed that the observed high NRR catalytic activity for the Fe SA-NO-C catalyst stemmed mainly from the optimizedc harge-transfer between the adjacent Oa nd Fe atoms homogenously distributed on the porous carbon support, which could not only significantly facilitate the transportation of N 2 and ions but also effectively decrease the binding energy between the isolated Fe atom and *N 2 intermediate and the thermodynamic Gibbsfree energy of the rate-determining step (*N 2 ! *NNH).

Promoting the formation of oxygen vacancies in ceria multishelled hollow microspheres by doping iron for enhanced ambient ammonia electrosynthesis

“…24 The electrocatalytic NRR (N 2 + 6H + + 6e − → 2NH 3 ) typically involves three elemental steps: (1) adsorption of N 2 molecules on the catalytically active sites (N 2 + * → *N 2 ); (2) cleavage of the NuN bonds and subsequent hydrogenation of N 2 (*N 2 + 6e − + 6H + → 2*NH 3 ); (3) desorption of the formed NH 3 molecules from the active sites. 6 Generally, the kinetics of the NRR is hindered by the inert adsorption of N 2 molecules and the huge energy barrier for cleaving the NuN bonds. [35][36][37] As for the NRR using Fe-CeO 2 HM, the coordination unsaturated Ce 3+ sites with high electron densities next to the oxygen vacancies could efficiently adsorb the free N 2 molecules by easily delivering electrons to the adsorbed N 2 molecules.…”

“…4 Up to now, varieties of catalysts have been employed to promote the electrochemical NRR, including noble-metal based materials, non-noble metal based materials and carbon-based materials. [5][6][7][8] Noble materials have shown remarkable activity, whereas high price and rarity limit its application. Therefore, much attention has been focused on non-noble-metal based catalysts, such as L-Co 3 O 4 -4.0 (Fe-WB 2 , V-NiS 2 , CeP-rGO, nanoporous NiSb, Zn/Fe-N-C).…”

“…Moreover, Fe, as the essential component of nitrogenases, has been widely applied in N 2 fixation processes including Haber-Bosch and electrochemical. 6 Thus, doping Fe has the potential to promote the formation of oxygen defects in CeO 2 , thereby improving the catalytic activity towards the NRR, which however are unexplored thus far.…”

Fe‐based catalysts for nitrogen reduction toward ammonia electrosynthesis under ambient conditions

“…(I) A proposed reaction mechanism for the conversion of N 2 to NH 3 . Reproduced with permission 37 . Copyright 2021, Wiley…”

Single metal atoms catalysts—Promising candidates for next generation energy storage and conversion devices

“…(B) Performance comparisons for Co‐N‐C and Co‐N‐PCNFs cathode catalysts in H 2 /air cells. (C) Fuel cell stability tests for Co‐N‐PCNFs cathode catalyst through voltage cycling between 0.6 and 0.95 V. (B, C) Reproduced with permission 96 . Copyright 2020, Wiley‐VCH.…”