AgCu Bimetallic Electrocatalysts for the Reduction of Biomass-Derived Compounds

Abstract

The electrochemical transformation of biomass-derived compounds (e.g., aldehyde electroreduction to alcohols) is gaining increasing interest due to the sustainability of this process that can be exploited to produce value-added products from biowastes and renewable electricity. In this framework, the electrochemical conversion of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)furan (BHMF) is studied. Nanostructured Ag deposited on Cu is an active and selective electrocatalyst for the formation of BHMF in basic media. However, this catalyst deserves further research to elucidate the role of the morphology and size of the coated particles in its performance as well as the actual catalyst surface composition and its stability. Herein, Ag is coated on Cu open-cell foams by electrodeposition and galvanic displacement to generate different catalyst morphologies, deepening on the particle growth mechanism, and the samples are compared with bare Ag and Cu foams. The chemical–physical and electrochemical properties of the as-prepared and spent catalysts are correlated to the electroactivity in the HMF conversion and its selectivity toward the formation of BHMF during electroreduction. AgCu bimetallic nanoparticles or dendrites are formed on electrodeposited and displaced catalysts, respectively, whose surface is Cu-enriched along with electrochemical tests. Both types of bimetallic AgCu particles evidence a superior electroactive surface area as well as an enhanced charge and mass transfer in comparison with the bare Ag and Cu foams. These features together with a synergistic role between Ag and Cu superficial active sites could be related to the twofold enhanced selectivity of the Ag/Cu catalysts for the selective conversion of HMF to BHMF, that is, >80% selectivity and ∼ 100% conversion, and BHMF productivity values (0.206 and 0.280 mmol cm –2 h –1 ) ca. 1.5–3 times higher than those previously reported.

Insights into the Electrochemical Reduction of 5‐Hydroxymethylfurfural at High Current Densities

“…The electrocatalytic tests are performed over an AgCu foam previously investigated by us. [16,32] Briefly, the electrocatalyst is made by arrays of bimetallic AgCu nanoparticles that evenly coat the foam surface, few dendrites develop in the pore and strut edges. Over this catalyst, the characteristic HMF reduction peak is observed in linear sweep voltammetry (LSV) at pH = 9.2 for the 0.02-0.10 m HMF concentration range.…”

“…The onset of HMF reduction is around 60 mV lower than the HER onset (see Figure 1 and Refs. [16,32]).…”

“…We have previously observed that the sintering is accompanied by a Cu-enrichment. [32] X-ray diffraction (XRD) patterns of the spent catalyst confirm the presence of Ag 0 . The Cu 2 O phase, observed in the fresh catalyst, disappears (Fig- ure 4d).…”

“…Ag/Cu electrodes were synthesized by electrodeposition in a single-compartment three-electrode cell controlled by a potentiostat/galvanostat Metrohm Autolab PGSTAT204, equipped with NOVA software as reported elsewhere. [32] Characterization techniques XRD analysis was carried out directly at the foam specimens using a PANalytical X'Pert diffractometer equipped with a copper anode (λ mean = 0.15418 nm) and a fast X'Celerator detector. Wide-angle diffractogram was collected over a 2θ range from 3 to 80°with a step size of 0.067°and counting time per step of 60.95 s.…”

“…In LSV, the potential was scanned from 0 to À 1.4 V vs. SCE (from 0.79 to À 0.61 V vs. RHE) at a scan rate of 1 mV s À 1 in the electrolytes without HMF and 5 mV s À 1 in those with HMF, as reported elsewhere. [32] Electrocatalytic reductions were performed: (i) galvanostatically at current densities of 5, 10, 25, 40, and 50 mA cm À 2 recording the electrode potential (note that the area used to calculate the surface area corresponds to both faces of the foam piece); ii) potentiostatically in the À 1.1 to À 1.5 V vs. SCE range (À 0.31 to À 0.71 V vs. RHE). The solution was kept under stirring, with a magnetic bar, at 1000 rpm.…”