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Background
There is an increasing demand for chlorine in the last several decades, and the worldwide chlorine production exceeds 60 million metric tons per year in 2013. The current state of the art in chlorine production involves electrolysis of sodium chloride using a membrane-based chlor-alkali technology where the cathode reaction involves hydrogen evolution. These state of the art membrane reactors are one of the most energy-intensive processes in the industry. Chlor-alkali electrolysis operates at a typical current density of 4 kA/m2 corresponding to 3.2 V, with the average electric power consumption per ton chlorine amounting to approximately 3.0 MWh. Moreover, this mature membrane technology is believed to have reached its theoretical limit, with the majority of the over voltage arising from the cathodic hydrogen evolution process at high pH. Recently, oxygen depolarized cathodes (ODCs) have become the most intensively studied alternative means to further reduce power consumption.
Technology Overview
This invention is a method of synthesizing an electrocatalyst for oxygen reduction reaction, the method including the steps of (a) mechanical activation of a first organic ligand, a first transition metal or salt thereof, and a acid or inorganic salt as catalyst with or without the presence of trace amount of solvent to form a product, such that the first catalytic precursor is a heteroatom-containing organic molecule, and such that the product includes a metal-organic framework (MOF) including the first transition metal; (b) incorporating a second transition metal or salt and a second organic ligand as filling/coating compound together with the product resulting from the second transition metal or salt as encapsulated inside or coated on the surface of the MOF; and subjecting the catalyst precursor resulting from (b) to pyrolysis, whereby the first transition metal evaporates (i.e., the first transition metal is volatile at the temperature of pyrolysis) yielding the electrocatalyst. In the embodiments of this method, there is no isolating step to separate the MOF precursor from other reaction components.
Benefits
This method is a facile, simplified approach to obtain the metal-organic framework (MOF) based catalysts for oxygen reduction reaction (ORR) with low cost and high reproducibility.
Applications
The electrocatalysts are applicable in various electrochemical systems, including oxygen depolarized cathodes (ODC) for chlorine evolution processes in chlor-alkali cells.
