NNadir's Journal - Electroreduction of CO2 on Glassy Carbon Using Porphyrin Modified Electrodes.

As is well known to people who have taken a science course in their lives, the vast majority of the reduction of carbon dioxide by living systems is dominated by the use of chlorophyll, which is structurally a porphyrin complex of magnesium.

Here is a picture of the chlorophyll porphyrin:

The source of energy for the reduction of carbon dioxide by chlorophyll is of course, solar energy, and, from a thermodynamic perspective, the energy efficiency is extremely low, less than 10%, sort of like the capacity utilization of solar PV toxicological nightmares, which seldom ever reaches 15%, which is why the fraudulent solar industry always advertises it's systems not in terms of energy but rather by peak power which solar PV systems never actually reach.

Live, From the Massachusetts Museum of Contemporary Art: The Solar System.

One Holy Grail in energy science is to achieve the efficient electrochemical reduction of carbon dioxide to energy carriers, which are chemically reduced compounds.

I found a relatively recent report in the scientific literature interesting in this regard since it involves porphyrin biomimetic chemistry to accomplish the reduction of carbon dioxide using electricity as a source of energy.

Here is the abstract of the paper to which I will refer:

Journal of Molecular Catalysis A: Chemical 229 (2005) 249–257

The title of the article as one can see by clicking on the link above is: "Electrochemical reduction of CO2 mediated by poly-M-aminophthalocyanines (M = Co, Ni, Fe): poly-Co-tetraaminophthalocyanine, a selective catalyst."

Here are some excerpts from the paper:

The electrochemical reduction of CO2 has been extensively studied due to its increasing concentration in the atmosphere generating the so-called “green house effect” which might cause undesirable changes in the environment. It presents the possibility of recycling and transforming this raw material into a source of carbon for chemicals or fuels <1–3>. This reaction has been studied on different electrodes;metallic cathodes such as Hg, Pb, Sn, In, Au, Ag, Pt, Ni and Cu <4–6> and semiconductors such as p-Si, p-CdTe, p-InP, p-GaP, n-GaAs <3,7,8>. Carbon electrodes have also been used but, in this case, the reaction requires high over potential and depending on the electrolyte, evolution of H2 could decrease the efficiency of the process <9–11>. However, it is possible to use carbon electrodes if transition metal complexes act as electronic mediators either in solution <12–17> or becoming modified electrodes <18–23>. Azamacrocycles like porphyrins or phthalocyanines containing different transition metals have been investigated showing good electrocatalytic behavior when forming parts of modified electrodes <24–32>. For these cases, the selectivity and efficiency will depend on the media, applied potential, and microenvironment among other factors <24–32>. In the last years the possibility of electropolymerizing azamacrocyclic complexes on carbon electrodes surfaces has also been studied <33,34>...

The porphyrin complexes used in this chemistry are not co-ordination complexes of magnesium, as chlorophyll is, but rather complexes of the metals cobalt, nickel and iron, which happen to be the most paramagnetic elements among the transition "d" elements. (Lanthanide paramagnetic elements such as samarium are also known.)

The South American scientists who have written this paper report the products of this reaction:

The results of the electrolysis experiments are summarized in Table 1. It is worth noticing that the active polymers
release protonated species, since it is frequently reported that phthalocyanines or porphyrins (of Co generally)<27–31> are selective catalyst for CO. Indeed the reaction
products for polymeric-polypyridine metallic complexes modified electrodes were exclusively formic acid and formaldehyde <18–20>.

In table one the only other product is hydrogen.

Formaldehyde and formic acid need to be further reduced to methanol or DME to be useful as fuels. This would best be accomplished by hydrogenation, but obtaining the hydrogen further reduces efficiency.

The efficiency for the reduction complex was highest for nickel pthalocyanine complexes, about 40%.

The best catalyst in this case was Ni-phthalocyanine, with a maximum current efficiency of 40% at −1.5V versus NHE. Selectivity is dependent on the metal center and the electrochemical potential used in the experiment. Formation of urea specifically depends on the ability of the metal center to form CO and ammonia separately.

The more I think about energy, by the way, the more I recognize the element nickel as being one of the most important elements in the periodic table for technological development. This metal has tremendous use both as a catalyst, where it is important in oxidation reduction chemistry, but also in the preparation of high temperature superalloys like Hastelloy and Inconel. It's a great metal.

I hope this report doesn't generate any "we and our stupid cars are saved" thinking, but it is interesting because of the electrochemical organic moieties.