Orthogonal Design of Fe−N₄ Active Sites and Hierarchical Porosity in Hydrazine Oxidation Electrocatalysts

Abstract

Hydrazine is a promising energy-dense fuel for alkaline fuel cells. To design efficient and affordable electrocatalysts for the hydrazine oxidation reaction (HzOR), one needs to control both the active site and the supporting scaffold. We now report a family of electrocatalysts for alkaline HzOR, consisting of atomically dispersed FeÀ N 4 sites (as iron corroles of varying sizes) on hierarchically porous, electronically conductive carbon scaffolds that were prepared by self-templating from a novel barium-based precursor. The orthogonal design of active sites and flow-enhancing scaffolds allowed the rational optimization of their combination, to achieve excellent HzOR activity. These catalysts demonstrate the utility and versatility of metallocorroles for electrocatalysis in the nitrogen cycle, as well as the importance of pore tuning for optimization of the current density.

Lanthanoid coordination compounds as diverse self-templating agents towards hierarchically porous Fe–N–C electrocatalysts

“…This contrasts all previously reported Fe–N–C HzOR electrocatalysts, where Fe is typically deactivated, resulting in a peak-shaped voltametric wave. 50,63,64 The atomical dispersion of the Fe–N x moieties is further supported by cyanide and nitrite poisoning experiments (Fig. S10, ESI†), which show lower current densities upon selective poisoning of iron centers.…”

“…This contrasts all previously reported Fe-N-C HzOR electrocatalysts, where Fe is typically deactivated, resulting in a peak-shaped voltametric wave. 50,63,64 The atomical dispersion of the Fe-N x moieties is further supported by cyanide and nitrite poisoning experiments (Figure S10), which show lower current densities upon selective poisoning of iron centers. 66,[86][87][88] Tafel analysis confirms a distinct change in electrocatalytic mechanism (Figure S11): the iron-free NC= materials show Tafel slopes of 270±70 mV/dec, whereas the iron-imprinted Fe-NC Ln catalysts exhibit steeper slopes of 140±25 mV/dec (Table S4).…”

“…Zn 2+ -N 4 or Mg 2+ -N 4 ), can be transmetalated by catalytic elements such as Fe 2+ . The resulting materials belong to the highly important class of atomicallydispersed Fe-N-C electrocatalysts, which show great promise in the oxygen, 50,[59][60][61][62] nitrogen, 50,[63][64][65][66][67][68] and carbon cycles. 69,70 This method is particularly useful for avoiding the formation of surface-blocking FeX particles during pyrolysis with iron precursors.…”

Milestones and Most Recent Advances in Corrole’s Science and Technology

“…Shahaf et al demonstrated a range of novel orthogonally designed hydrazine oxidation electrocatalysts with iron corroles as molecular catalysts. 155 The iron(III) corroles that were tested are meso-C-substituted with CF 3 , C 6 F 5 , or 2,6difluorophenyl. These are listed in the order of electronwithdrawing capability, and the former complex is also much smaller than the other two.…”

“…HzOR electrocatalysis was since reported on many carbon-adsorbed metallo­phthalo­cyanines, while metallocorroles were tested most recently. Shahaf et al demonstrated a range of novel orthogonally designed hydrazine oxidation electrocatalysts with iron corroles as molecular catalysts . The iron­(III) corroles that were tested are meso -C-substituted with CF 3 , C 6 F 5 , or 2,6-difluorophenyl.…”