(Invited) Nanostructured Multimetallic Materials for Selective Biomass Electroreforming

Abstract

Facing the depletion of fossil resources and the environmental issues related to their use, the modern society has to develop eco-processes for the conversion of biomass either into fuels for energy production, conversion and storage applications and/or into platform molecules.Cellulose and hemicelluloses, represent 40 to 60 wt% of agriculture green wastes, and can be considered as raw materials. After transformation of these biopolymers into saccharides, they can serve as platform molecules for the production of chemicals with high value added and/or industrial interest.Hydrogen is currently mainly produced from reforming reactions of non-renewable fossil fuels, mainly natural gas, leading to reformate containing carbon monoxide. Carbon monoxide strongly poisons fuel cell catalysts, so that reformate has to be purified, which make the production process very complex, energy consuming and costly. Water electrolysis has been proposed as an alternative for the production of high-purity hydrogen, but the energy needed for the water splitting is high (DG° = 237 kJ mol-1) leading to cell voltage higher than 1.5 V, i.e. high electrical energy consumption. This makes electrolytic hydrogen production too expensive to compete with natural gas steam reforming processes.The conversion of biomass, polyols and sugars, by electrochemical methods can be performed in aqueous media at low temperatures, low pressures and low electrode potentials. The control of the electrode and the adequate formulation of catalysts lead to improve the conversion rate and the selectivity of the reaction. Moreover, the biomass conversion at the anode of an electrolysis cell can performed simultaneously with the production of pure hydrogen at the cathode, with a cell voltage lower than 0.6 V, i.e. with an energy saving of more than 50 % compared with water electrolysis. Hydrogen may be stored for further energy conversion in a fuel cell, or used as chemical reagent for further chemical hydrogenation reactions.Such system can have a huge industrial interest if the anodic catalyst displays the following properties: high activity at very low electrode potentials, high selectivity towards a given product, high faradaic efficiency for the oxidation reaction and high stability under operating conditions.Here, the synthesis and characterization of Pd- and Pt-based binary catalysts will be presented and their electrocatalytic behavior towards polyols oxidation will be first studied by linear scan voltammetry in a classical three-electrode cell to evaluate their activity and by in situ infrared spectroscopy to determine reaction intermediates and product as a function of the electrode potential. Best candidates will be used as anode catalysts to perform the polyols electroreforming in a two-electrode electrolysis cell with simultaneous production of hydrogen at the cathode. Reaction products will be analyzed by HPLC, MS and 1H and 13C NMR to determine the selectivity and the efficiency of the system.