An electrochemical process for preparing a compound comprising a metal or metalloid and a peroxide, ionic or radical species

Abstract

An electrochemical process is for recovering a metal element or a metalloid element or a mixture of two or more thereof from at least one water soluble precursor compound containing the metal element or a metalloid element or two or more thereof, in the form of one or more nano particles, in particular nano crystals of at least one reaction product. The process includes supplying the water soluble precursor compound to a water-based catholyte of a cathode compartment of an electrochemical cell, equipped with a cathode containing a gas diffusion electrode, adjusting the pH of the catholyte, supplying at least one oxidant gas to the gas diffusion electrode, and subjecting the cathode to an electrochemical potential to cause reduction of the at least one oxidant gas.

1 . An electrochemical process for recovering reaction products of a metal element or a metalloid element or a mixture of two or more thereof from at least one water soluble precursor compound comprising the metal element or the metalloid element or two or more thereof, in the form of nano particles, in particular nano crystals of at least one reaction product, wherein the process comprises:
 supplying a solution of the water soluble precursor compound to a water-based catholyte of a cathode compartment of an electrochemical cell, equipped with a cathode comprising a gas diffusion electrode, wherein the gas diffusion electrode comprises a porous electrochemically active material having a BET surface area of at least 50 m 2 /g,   adjusting the pH of the catholyte to a pH which is smaller than the pKa of the water soluble precursor compound,   supplying at least one oxidant gas to the gas diffusion electrode,   subjecting the cathode to an electrochemical potential to cause reduction of the at least one oxidant gas to one or more of the corresponding peroxide, ionic and/or radical reactive species capable of reacting with a cation comprising the metal element, or the metalloid element or the mixture of two or more thereof, to nano particles of the at least one reaction product with an average particle size, in particular nano crystals with an average crystallite size, equal to or smaller than 30.0 nm.   
     
     
         2 . The process as claimed in  claim 1 , wherein the at least one water soluble precursor compound comprises the metal element or the metalloid element in the form of a cation of the metal or the metalloid element, or the at least one water soluble precursor compound comprises a cation comprising the metal element or the metalloid element or the mixture of two or more thereof, or the at least one water soluble precursor compound comprises a mixture of two or more of the afore mentioned compounds. 
     
     
         3 . The process as claimed in  claim 1 , wherein the oxidant gas is an inorganic oxidant gas or a mixture of two or more of such gases. 
     
     
         4 . The process as claimed in  claim 3 , wherein the inorganic oxidant gas is selected from the group consisting of ozone, oxygen, carbon oxides, nitrogen oxides, halogen oxides, sulfur oxides, halogens, air, biogas, flue gas, acid gas, combustion exhaust gas, or a mixture of two or more of the afore mentioned gases or a mixture of two or more of the afore mentioned oxidant gases. 
     
     
         5 . The process according to  claim 1 , wherein a supply rate with which the oxidant gas is supplied to the gas diffusion electrode is variable. 
     
     
         6 . The process according to  claim 1 , wherein a partial pressure of the oxidant gas that is supplied to the gas diffusion electrode is variable. 
     
     
         7 . The process as claimed in  claim 1 , wherein the at least one water soluble precursor compound is supplied to the water-based catholyte as a solution of the water soluble precursor in water. 
     
     
         8 . The process as claimed in  claim 1 , wherein the at least one water soluble precursor compound is supplied to the water-based catholyte as a solid, and is at least partly dissolved in the catholyte. 
     
     
         9 . The process as claimed in  claim 1 , wherein a concentration of the at least one water soluble precursor compound supplied to the water-based catholyte is variable. 
     
     
         10 . The process as claimed in  claim 1 , wherein the catholyte has an ionic conductivity of at least 1.0 mS/cm. 
     
     
         11 . The process as claimed in  claim 1 , wherein the electrochemically active material comprises an active surface having at least one weak acid or weak basic functional group or a mixture of at least one weak acid and weak basic group. 
     
     
         12 . The process as claimed in  claim 1 , wherein a hydrophilic side of the electrochemically active surface of the gas diffusion electrode encompasses a plurality of functional groups which may be polarized or deprotonated upon application of the electrochemical potential. 
     
     
         13 . The electrochemical process as claimed in  claim 1 , wherein in advance of supplying the water soluble precursor compound to the cathode compartment, the pH of the catholyte is adjusted to a pH≦7, preferably to a pH≦5. 
     
     
         14 . The electrochemical process as claimed in  claim 1 , wherein an aqueous solution of a weak protonic electrolyte is supplied to the catholyte, preferably a weak protonic base or a weak protonic acid, more preferably a weak polyprotonic base or a weak polyprotonic acid. 
     
     
         15 . The electrochemical process as claimed in  claim 14 , wherein the weak protonic acid has a pKa which is at least one unit higher than the pH of the catholyte. 
     
     
         16 . The electrochemical process as claimed in  claim 14 , wherein the weak protonic base has a pKa of between 6.0 and 12.0, preferably between 7.0 and 11.0. 
     
     
         17 . The electrochemical process as claimed in  claim 1 , wherein the electrochemically active material has a BET surface area of at least 100 m 2 /g, preferably at least 200 or 250 m 2 /g, more preferably at least 400 or 500 m 2 /g, most preferably larger than 750 or 1000 m 2 /g. 
     
     
         18 . The electrochemical process as claimed in  claim 1 , wherein a binary electrolyte is supplied to the catholyte with the purpose of raising an electric conductivity of the catholyte, preferably raising an electric conductivity of the catholyte to at least 5 mS·cm −1 , more preferably between 20 and 80 mS·cm −1 , most preferably between 20 and 50 mS·cm −1 . 
     
     
         19 . The electrochemical process as claimed in  claim 18 , wherein the binary electrolyte is a water soluble ionic salt or a mixture of two or more of such salts, but preferably the binary electrolyte is sodium chloride, 
     
     
         20 . The electrochemical process as claimed in  claim 1 , wherein an ionic liquid is supplied to the catholyte, in a molar ratio of at least 10:1 with respect to the water soluble precursor compound, with the purpose of producing nanocrystals containing the ionic liquid or one or more of its decomposition products. 
     
     
         21 . The electrochemical process as claimed in  claim 20 , wherein the ionic liquid is a hydrophilic ionic liquid, preferably tetrabutylammonium chloride or tetrabutyl ammonium bromide. 
     
     
         22 . The electrochemical process as claimed in  claim 1 , wherein the electrochemical potential to which the cathode is subjected is a reducing potential relative to a reference electrode, which is below the thermodynamic pH potential equilibrium region of stability of the oxidant gas in water, preferably below the region of thermodynamic stability of water, more preferably outside of the region of thermodynamic stability of hydrogen. 
     
     
         23 . The electrochemical process as claimed in  claim 1 , wherein the precursor compound is a compound of an ion of an element selected from the group consisting of group I, II, III and IV elements of the periodic table of elements, transition metal elements, actinides and lanthanides and a compound containing two or more of such elements. 
     
     
         24 . The electrochemical process as claimed in  claim 1 , wherein the electrochemical potential to which the cathode is subjected is reversed with the purpose of recovering the nano crystals from an electrochemical active porous material at the gas-diffusion cathode. 
     
     
         25 . The electrochemical process as claimed in  claim 1 , wherein one or more additives are supplied to the catholyte, the one or more additives being selected from the group consisting of dispersants, stabilizers, surfactants, polymers, copolymers, emulsifiers, cross-linking agents, capping agents and free flow agents and a mixture of two or more of these compounds. 
     
     
         26 - 31 . (canceled) 
     
     
         32 . A method for selectively isolating a reaction product of at least one metal element or a metalloid element or two or more thereof from an aqueous solution comprising a water soluble precursor compound thereof, wherein use is made of the process as claimed in  claim 1 . 
     
     
         33 . (canceled) 
     
     
         34 . The process as claimed in  claim 1 , wherein the electrochemically active material comprises at least one weak protonic acid or weak protonic basic functional group or a mixture of at least one weak protonic acid and weak protonic basic group. 
     
     
         35 . The process as claimed in  claim 12 , wherein the functional groups contain one or more moieties selected from the group consisting of a nitrogen containing moiety, an oxygen containing moiety, a chlorine containing moiety and a sulfur containing moiety.