Designing molecular catalysts for proton reduction and water oxidation
Title: Designing molecular catalysts for proton reduction and water oxidation
DNr: SNIC 2015/1-96
Project Type: SNIC Medium Compute
Principal Investigator: Sascha Ott <sascha.ott@kemi.uu.se>
Affiliation: Uppsala universitet
Duration: 2015-04-01 – 2016-04-01
Classification: 10404 10405
Homepage: http://www.kemi.uu.se/Research/principal-investigators/sascha-ott/
Keywords:

Abstract

A steady increase of energy demand has made dearth of fossil fuels an unavoidable problem. The high efficiency of the solar energy scheme which is a credible alternative to fossil fuels has encouraged the hunt for efficient water oxidation and carbon dioxide reduction catalysts. In order to design active catalysts, proper understanding of the catalytic pathway is of prime importance. This project emphasizes therefore on understanding a) photo induced catalytic water oxidation pathways using Iron catalysts and b) electrocatalytic carbon dioxide reduction using Ruthenium catalysts. a) Solar energy induced water splitting process requires the coupling of the two half-reactions: (i) oxidation of H2O to generate the reducing equivalents (Oxygen, protons and electrons) and (ii) reduction of protons to molecular hydrogen. As water oxidation is the bottle neck of this process, development of water oxidation catalysts (WOC) have been exhilarated. Quite many Ruthenium and Iridium complexes have been reported till date to be active in this catalytic process and can be useful in understanding the catalytic pathways which are pivotal developing better catalysts; but extensive use of such metals brings some of the obstacles such as being expensive and toxic. To be able to use widely, we need to concentrate on earth abundant, cheap first row transition metals which can sustain multiple redox levels. Fulfilling the above mentioned criteria, Iron complexes exemplify a prospective candidate. Although few iron complexes have been reported till date to catalyze water oxidation with reasonable TON, the complete mechanism is yet to be revealed. In this quest we have been investigating robust Fe-pyridyl complexes. As the preliminary catalytic water oxidation results (both chemical driven and light driven) are very promising, detail mechanistic investigations are being commenced to proceed towards developing improved catalysts. b) CO2 reduction serves as one of the renewable carbon-neutral sources to produce low-carbon products such as CO, HCOOH, CH3OH and CH4. CO is one of the components of water gas (CO+H2O) which is presently combined with gasification of coal to produce pure hydrogen industrially. HCOOH is one of the most promising materials of hydrogen storage today since it readily decomposes into H2 and CO2 in the presence of a suitable catalyst. CH3OH has an advantage of being a liquid at room temperature. Methane is more easily stored than hydrogen. Thus CO2 reduction can also be readily employed on commercial scale to meet the urgent requirements of alternative renewable sources of energy. Designing catalysts for CO2 reduction is still in its preliminary stage and is a blooming area of research. As stated above, to build efficient catalysts, the understanding of mechanistic details (energies and nature of transition states and intermediates) is very important and for that computational tools are essential. Some of the ruthenium complexes synthesized by our group have shown promising catalytic activity towards CO2 reduction as seen via various experiments. In order to understand the nature and energetics of the transition states and CO2 bound intermediates involved in these reactions, computational investigations need to be done.