Conversion of liquid co2

Abstract

A method for electrochemically reducing carbon dioxide includes the step of providing a liquid or supercritical carbon dioxide mixture comprising liquid or supercritical carbon dioxide, water, a phase transfer catalyst, and an ion conducting salt. A potential difference is applied across a portion of the liquid or supercritical carbon dioxide mixture to cause the reduction of carbon dioxide with protons from the water. A reactor for electrochemically reducing carbon dioxide is also disclosed.

We claim: 
     
         1 . A method for electrochemically reducing carbon dioxide, comprising the steps of:
 providing a liquid or supercritical carbon dioxide mixture comprising liquid or supercritical carbon dioxide, water, a phase transfer catalyst, and an ion conducting salt; and,   applying a potential difference across a portion of the liquid or supercritical carbon dioxide mixture to cause the reduction of carbon dioxide with protons from the water.   
     
     
         2 . The method of  claim 1 , wherein the potential difference is applied by electrodes, the cathode comprising at least one selected from the group consisting of molybdenum, carbon fiber, copper, nickel, metal carbides, metal borides, titanium and aluminum, and the anode comprising platinum, iridium oxide, or a material capable of the oxygen evolution reaction (OER). 
     
     
         3 . The method of  claim 1 , wherein the potential difference is applied by electrodes comprising molybdenum. 
     
     
         4 . The method of  claim 3 , wherein the electrodes comprise molybdenum and MoO 2 . 
     
     
         5 . The method of  claim 3 , wherein the electrodes comprise 5 atomic percent to 100% molybdenum. 
     
     
         6 . The method of  claim 1 , wherein the electrodes have a porosity of from 15 to 90%. 
     
     
         7 . The method of  claim 1 , wherein the electrodes comprise a material that is electrochemically stable (−2.5 V to 0 V versus a standard hydrogen electrode (SHE)) and supercritical carbon dioxide stable. 
     
     
         8 . The method of  claim 1 , wherein the ion conducting salt comprises a cation selected from the group consisting of tetraethylammonium, tetrabutylammonium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, and 1-hexyl-3-methylimidazolium, and an anion selected from the group consisting of iodide, hexafluorophosphate, tetrafluoroborate, bis(trifluoromethane) sulfonimide, and triflate (trifluoromethanesulfonate). 
     
     
         9 . The method of  claim 1 , further comprising at least one reaction promoting salt. 
     
     
         10 . The method of  claim 9 , wherein the reaction promoting salt comprises at least one selected from the group consisting of CsTFSI, CsOTf, CsOAc, CsI, Cs 2 CO 3 , CsF, CsCl, KTFSI, KOTf, KOAc, KI, K 2 CO 3 , KF, and KCl. 
     
     
         11 . The method of  claim 1 , wherein the phase transfer catalyst comprises at least one selected from the group consisting of acetonitrile, succinonitrile, monoglyme, diglyme, triglyme, tetraglyme, tetrahydrofuran (THF), dioxolane, and 1-octanol. 
     
     
         12 . The method of  claim 1 , wherein the product of the electrochemical reduction of the carbon dioxide is at least one selected from the group consisting of ethanol, propane, methanol, isopropanol, ethylene, acetone, and carbon monoxide. 
     
     
         13 . The method of  claim 1 , wherein the supercritical carbon dioxide mixture comprises from 10 to 95 wt % carbon dioxide, 5 to 80 wt % water, 5 to 70 wt % phase transfer catalyst, 1 to 50 wt % ion conducting salt, and 1 to 50 wt % reaction promoting salt. 
     
     
         14 . The method of  claim 1 , wherein the pressure of the liquid carbon dioxide mixture is from 100 to 1070 psi, and the pressure of the supercritical carbon dioxide mixture is from 1070 psi to 1500 psi. 
     
     
         15 . The method of  claim 1 , wherein the temperature of the supercritical carbon dioxide mixture is from 40 to 100° C. 
     
     
         16 . The method of  claim 1 , wherein the potential applied to the electrodes is from −2 to −0.5 V versus an Ag/AgCl reference. 
     
     
         17 . A reactor for electrochemically reducing carbon dioxide, comprising a reactor vessel for containing a supercritical carbon dioxide mixture comprising liquid or supercritical carbon dioxide, water, a phase transfer catalyst, and an ion conducting salt, the reactor having electrodes for applying a potential difference across a portion of the liquid or supercritical carbon dioxide mixture, the electrodes comprising an electrode composition comprising from 5 atomic percent to 100 atomic percent molybdenum. 
     
     
         18 . The reactor of  claim 17 , wherein the electrode is comprised of molybdenum and MoO 2 . 
     
     
         19 . The reactor of  claim 17 , wherein the electrode is the cathode and comprises 5 to 100 atomic % molybdenum.