The climate crisis has come to the attention of many scientists, lawmakers, and global companies in recent years. Replacing petrochemicals with refined waste biomass as a sustainable chemicals source has become an attractive option to lower global carbon emissions. Popular methods of refining lignocellulosic waste biomass use thermochemical means which have significant environmental downsides, that can be overcome by using electrochemistry instead. This can revolutionise the way many chemicals are produced today.
Guided by theoretical calculations, this work begins by demonstrating the electrochemical production of the biofuels 2-methylfuran and hydrofuroin via the electroreduction of furfural, using synthesised single-atom electrocatalysts, and Cu foil electrodes. This study revealed that a proton-coupled electron transfer (PCET) mechanism is the favoured method of electrochemical reduction under acidic (pH 1) conditions.
New electrochemical processes to produce amines from 5-hydroxymethylfurfural (HMF) are explored using hydroxylamine as a nitrogen source, in an electrochemical reductive amination reaction. A range of metal surfaces were tested with Ag electrodes exhibiting the best reductive amination activity in mild, aqueous conditions. A new electrochemical synthesis process is demonstrated whereby an amino acid 5-(aminomethyl)furan-2-carboxylic acid (AFCA), is produced by combining Ag cathodes with MnOx anodes to independently convert the functional groups of HMF without the need to separate intermediates between reactions.
Lastly, the development of a new metal-free electrocatalyst is detailed by immobilising (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) onto an electrode surface, aiming to oxidise HMF into the monomer 2,5-furandicarboxylic acid (FDCA). For the first time in literature, selective electrochemical production of 5-formyl-2-furoic acid (FFCA) is successfully reported. Methods are discussed to try and steer the selectivity from FFCA to FDCA, which can be used as a replacement monomer for terephthalic acid in PET polymers.
Due to the significance of the work presented here, the commercialisation of electrochemical biomass valorisation is brought a step closer.