Nickel and Nitrogen-Doped Bifunctional ORR and HER Electrocatalysts Derived from CO₂

Abstract

While nonprecious metal catalysts (NPMCs) have been shown to be viable alternatives for Pt-based catalyst materials in both proton exchange membrane fuel cells (PEMFCs) and electrolyzers, all of the synthesis methods of these materials still have a positive carbon footprint. This means that, while the production of CO 2 is avoided by converting to a hydrogen economy, a large amount of CO 2 must be produced to drive this transition (as much as 600 kg of CO 2 per kilogram of catalyst for CVD-based materials). Here, we demonstrate, for the first time, a sustainable method for synthesizing a bifunctional oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalyst directly from CO 2 in a process that captures carbon dioxide from the atmosphere or flue gases instead of producing it as all previous methods for creating ORR/HER catalysts. The electocatalytic activity of the material is correlated to its structure and synthesis conditions by a thorough physicochemical analysis including rotating disk electrode (RDE) measurements, porosity analysis with N 2 physisorption, scanning and transition electron microscopy imaging (SEM, TEM) and X-ray analysis of the materials' crystal structure and elemental composition. The material shows promising activity and paves way for a dual approach on reducing the CO 2 footprint of the energy economy.

A MnOx–graphitic carbon composite from CO2 for sustainable Li-ion battery anodes

“…1.0 V. These processes are ascribed to the reduction of Mn 4+ to Mn(0) and to the oxidation of metallic Mn to Mn 2+ . The further oxidation of Mn 2+ occurs at potentials higher than 2 V. 32 In the 2nd CV, the reduction broad peak shifts at ca. 0.5 V and remains constant also for the following cycles, indicating the conversion of the Mn 2 O 3 and MnO 2 phases (observed in XPS) to MnO.…”

“…The carbon is synthesized from CO 2 using the molten salt CO 2 capture and electrochemical transformation (MSCC-ET) method 3,30 which Ratso et al have previously used to synthesize CO 2 -derived catalyst materials. 31–34 The method is based on capturing CO 2 into molten carbonate salts, where CO 3 2− is in equilibrium with CO 2 in the surrounding atmosphere: CO 3 2− ⇄ CO 2 + O 2− or CO 2 + CO 3 2− ⇄ C 2 O 5 2− . In turn, CO 3 2− is electrochemically split into carbon and oxygen by a four-electron transfer process: CO 3 2− + 4e − ⇄ C + 3O 2− .…”

“…1.0 V. These processes are ascribed to the reduction of Mn 4+ to Mn(0) and to the oxidation of metallic Mn to Mn 2+ . The further oxidation of Mn 2+ occurs at potentials higher than 2 V [32] . In the 2nd CV, the reduction broad peak shifts at ca.…”

“…The carbon is synthesized from CO 2 using the molten salt CO 2 capture and electrochemical transformation (MSCC-ET) method [3,30] which Ratso et al has previously used to synthesize CO 2derived catalyst materials [31][32][33][34] . The method is based on capturing CO 2 into molten carbonate salts, where the CO 3 2is in equilibrium with CO 2 in the surrounding atmosphere:…”

Recent Advances Regarding Precious Metal-Based Electrocatalysts for Acidic Water Splitting

“…Some people have even proposed a very active direct synthesis of HER catalysts with Ni and N co-doping from CO 2 . A clean transition from a carbon-based economy to a hydrogen-based economy is achieved by comparing the physical qualities and electrocatalytic activities of carbon compounds generated from CO 2 [ 128 , 129 ].…”