The photoelectrocatalytic reduction of carbon dioxide

The kinetics of the photoreduction of CO{sub 2} in nonaqueous solutions containing tetraalkyl ammonium cations has been examined with reference to the effects of surface decoration of p-CdTe with metals, organic complexes, and crown ethers. The electrode surface was scanned by SEM,XPS, and particularly by FTIR spectroscopy. The principle product throughout was CO, although small amounts of formate and methanol were observed. Catalysts, except for the crown ethers, produce an anodic shift in the i-V curves which is in the region of 100-200 mV, equivalent to {approx} 10 times increases in the rate constant. The efficiency of the conversion of light to CO is {approx} 5%. Crown ethers adsorb on the surface in a lying down position and behave in a pseudo-Langmuirian way. The 18-crown-6 ether in the presence of tetraethyl ammonium cations produce on the greatest catalysis, a 410 mV shift, equivalent to about 10{sup 3} times increase in the rate constant. The photoelectrochemical kinetic parameters are consistent with a rate-determining step, CO{sub 2} + H + e + hv {r arrow} CO + OH. The catalyst effect of the NR{sub 4} ions is interpreted in terms of the foregoing electrochemical reactions, NR{sub 4} + e {l reversible} NR{sub 4} and NRA + CO{sub 2} {r reversible} NR{sub 4} + CO{sub 2} which take place on different sites from that of the photoelectrochemical reactions. The catalytic shifts are correlated with changes in bonding between intermediate radicals and the catalyst atoms as in electrochemical catalysis.