Molten salt as ultrastrong polar solvent enables the most straightforward pyrolysis towards highly efficient and stable single-atom electrocatalyst

Currently,pyrolysis as the most widely used method still has some key issues not well resolved for synthesis of carbon-supported single-atom catalysts(C-SACs),e.g.,the sintering of metal atoms at high temperature as well as the high cost and complicated preparations of precursors.In this report,molten salts are demonstrated to be marvellous medium for preparation of C-SACs by pyrolysis of small molecular precursors(ionic liquid).The ultrastrong polarity on one hand establishes robust interaction with precursor and enables better carbonization,resulting in largely enhanced yield.On the other hand,the aggregation of metal atoms is effectively refrained while no nanoparticle or cluster is formed.By this strategy,a C-SAC with atomically dispersed Fe-N_(4) sites and a high specific area over 2000 m^(2) g^(-1) is obtained,which illustrates high ORR activity in both acid and alkaline media.Moreover,this SAC exhibits superior methanol tolerance and stability after acid soaking at 85℃ for 48 h.It is believed that the molten-salts-assisted pyrolysis can be developed into a routine strategy as it not only can largely simply the synthesis of C-SACs,but also can be extended to prepare other types of SACs.

Asymmetrically ligated single atomic nickel sites for efficient hydrogen peroxide electrosynthesis

Atomic transition-metal-nitrogen-carbon electrocatalysts hold great promise as alternatives to benchmark Pt in the oxygen reduction reaction.The pristine metal centers with quasi square-planar D_(4h) configuration,however,still suffer from unfavorable energetics and thereby strong activity/selectivity trade-off during the catalytic process.Here we present a ligand-field engineering of single-atom Ni-N-C catalysts to boost the sluggish kinetics via rationally constructing prototypical asymmetrically ligated Ni-N_(3)O_(1) sites.The as-obtained Ni-supported multi-walled carbon nanotubes with molten salt-treated(defined as Ni/CNS)catalyst delivered an excellent H_(2)O_(2) selectivity(>90%)within a wide potential window(0.2–0.7 V vs.reversible hydrogen electrode(RHE))and robust stability(for 10 h)in alkaline medium.Combined electron paramagnetic resonance and theoretical analysis rationalize this finding and demonstrate that the broken symmetry facilitates the electron transfer of a σ* to O–O orbital as compared to the Ni-N_(4) counterpart,playing an indispensable role in efficient O_(2) activation.