Active sites engineering leads to exceptional ORR and OER bifunctionality in P,N Co-doped graphene frameworks

Abstract

Bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are highly desirable for rechargeable metal-air batteries and regenerative fuel cells. However, the commercial oxygen electrocatalysts (mainly noble metal based) can only exhibit either ORR or OER activity, and also suffer from inherent cost and stability issues. It remains challenging to achieve efficient ORR and OER bifunctionality on a single catalyst. Metal-free structures offer relatively large scope for such bifunctionality to be enginnered within one catalyst, together with improved cost-effectiveness and durablility. Herein, by closely coupled computational design and experimental development, highly effective bifunctionality is achieved in a phosphorus and nitrogen co-doped graphene framework (PNGF) - with both ORR and OER activities reaching the theoretical limits of metal-free catalysts, superior to the noble metal counterparts in both (bi)functionality and durability. In particular, with the identification of active P-N sites for OER and N-doped sites for ORR , we successfully intensified such sites by one-pot synthesis to tailor the PNGF. The resulting catalyst reaches an ORR potential of 0.845 V vs. RHE at 3 mA cm-2 and an OER potential of 1.55 V vs. RHE at 10 mA cm-2, respectively. Its combined ORR and OER overpotential of 705 mV is significantly lower than those reported previously for metal-free bifunctional catalysts

Synthesis of Fe, Co Incorporated in P-Doped Porous Carbon Using a Metal-Organic Framework (MOF) Precursor as Stable Catalysts for Oxygen Reduction Reaction

“…Second, the P doped porous carbon will change the symmetry of the carbon atomic spin density to improve the ORR activity. 12,13,37 Furthermore, the P-O-Fe or P-O-Co bonds will further modify the electronic structure. 24,25,38 Finally, the synergistic effect of the transition metals is beneficial for the reactant adsorption and reduction at the catalyst surface.…”

Synthesis of Bimetallic Conductive 2D Metal–Organic Framework (CoxNiy‐CAT) and Its Mass Production: Enhanced Electrochemical Oxygen Reduction Activity

“…Therefore, the development of new electrocatalysts for the ORR to replace platinum‐based catalysts is quite important. Porous carbon‐based ORR catalysts with heteroatom‐doping (such as nitrogen, phosphorous, and cobalt) are one of the attractive candidate materials for replacing platinum‐based catalysts . By the way, metal–organic frameworks (MOFs) are typically porous materials which are widely used in gas storage, separation, catalysis, and sensing applications .…”

N, P Co‐doped Hierarchical Porous Graphene as a Metal‐Free Bifunctional Air Cathode for Zn−Air Batteries

“…[16] The active sites initiating the OER was the carbon atoms sits between N and C=O (ketone group), which has positive charge facilitate the adsorption of OH À and initiate the water oxidation. [18] The N and P co-doped mesoporous carbon aerogels has significantly improved activity in rechargeable ZnÀair batteries. Therefore, except for N doping, the introduction of multiple heteroatoms on metal-free catalyst which has lower electronegativity is of key importance to achieve high electrocatalytic bifunctionality.…”

“…Rotating ring-disk electrode (RRDE) voltammograms of the NPHG-8 at 1600 rpm (Figure 3f) indicate an electron transfer number (n) of ca. [18] The electrocatalytic activity of NPHG-8 has been demonstrated in both primary (two-electrode) and secondary (threeelectrode) ZnÀair battery prototype. These results are consistent with the previous reports of core-shell N,P,O co-doped carbon nanoparticles, [24] Ocontaining (e. g., quinone group [25] ) carbon, and pyridinic N doped graphene.…”