Noble-Metal-Free MOF-74-Derived Nanocarbons: Insights on Metal Composition and Doping Effects on the Electrocatalytic Activity Toward Oxygen Reactions

The continuous and dramatic increase of global demand for energy resources makes it urgent to develop affordable nanostructured materials to act as efficient electrocatalysts (ECs) in the energy-related reactions. Metal-organic framework (MOF) template pyrolysis for the production of nanostructured carbon-based materials is a very promising methodology to produce carbon-based ECs. Herein, we report the preparation, characterization (XPS, CHNS analysis, ICP-OES, XRD, TEM, and SEM/EDS), and application as oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) ECs of a plethora of nanostructured carbon materials derived from RT-synthesized (RT, room temperature) MOF-74 with different metal compositions, Co, Ni and Co/Ni, and dopant heteroatoms, N-, S- and N/S-dual-doping. This has allowed the study of the aforementioned parameters' influence on the OER and ORR electrocatalytic activity in alkaline medium. Highly synergetic effects have been detected in two cases: (1) when N/S-dual-doped carbon is produced from a monometallic Co-MOF-74 template, N,S-Co@C, and (2) when an undoped carbon is derived from bimetallic Co/Ni-MOF-74, Co/Ni@C. These two samples achieve OER performances with eta(10) = 0.41 and 0.44 V, respectively, along with Tafel slopes of 101 and 93 mV dec(-1), being close to the state-of-art OER catalyst performance. In addition, ORR tests showed that the effect of heteroatom doping on ORE, activity is always positive, regardless of metal composition.