Materials which show satisfying electrocatalytic activities for Hydrogen Evolution Reaction (HER) or Oxygen Reduction Reaction (ORR) for fuel cell energy storage are mainly based on Platinum which has a very limited abundancy. Although a few chalcogenides, such as MoS₂ or MnO₂ show promising catalytic activity, it is inherently limited by the accessible surface area of these materials. Over the last decade, hybrid porous materials (or Metal-Organic Frameworks) with intrinsic electronic conductivity have been reported.¹ MOFs potential assets as electrocatalysts are mainly due to the combination of three factors: i) Their crystalline nature allows a fine control of the spatial layout of active sites over a long range order, and potentially the tuning of conductivity. ii) Their hybrid nature gives rise to a very versatile chemistry and thus permits the systematic investigation of how both organic and inorganic counterparts influence on the material properties. iii) Their porosity provides a high density of accessible active sites.

Among electrically conductive MOFs, 2D triphenylene-based frameworks are of particular interest owing to their large π-conjugated systems and the resulting large conductivities. ^2-4 Indeed, a hexaimino-triphenylene/Ni^II MOF system (Ni-HITP) was recently reported to show great electrocatalytic activity towards ORR.⁵

Although a few tricatecholate MOFs based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and M^II cations (Co, Ni, Cu) have been reported,⁴ none of these have been tested for ORR electrocatalysis. We thus decided to investigate this system and isolated a previously unreported phase: Ni-HHTP-S which consists solely of 2D layers stacked in a staggered manner with blocked porosity. Interestingly, when thermally treated, Ni-HHTP-S undergoes a phase transition towards Ni-HHTP-E with eclipsed layers and accessible porosity. Both materials show different and high electrocatalytic activities towards ORR. This system thus offers a great opportunity to investigate the modulation of conductivity and catalytic activity of a 2D MOF, not only by its primary structure, but also by the secondary arrangement of its layers.This communication will present the frameworks characterizations and discuss their electronic conductivities and ORR electrocatalytic activities.

[1] L. Sun et al., Angew. Chem. Int. Ed., 2016, 55, 3566-3579.

[2] D. Sheberla et al., J. Am. Chem. Soc., 2014, 136, 8859-8862.

[3] M. Campbell et al., Angew. Chem. Int. Ed., 2015, 127, 4423-4426.

[4] M. Hmadeh et al., Chem. Mater., 2012, 24, 3511-3513.

[5] E. Miner et al, Nat. Commun., 2016, 7, 10942.