Cobalt nickel boride as electrocatalyst for the oxidation of alcohols in alkaline media

A mixed Co and Ni boride precursor was synthesized via chemical reduction and subsequently annealed at 400 or 500 °C with or without prior addition of the monomer benzoxazine (BO). The resulting mixed CoNiB materials were investigated as electrocatalysts for three alcohol oxidation reactions (AOR) in alkaline electrolyte: the oxidation of glycerol (GOR), ethylene glycol (EGOR) and ethanol (EOR). Comparison of the rotating disk electrode (RDE) cyclic voltammograms for the different catalysts revealed that CoNiB annealed at 500 °C without the addition of BO exhibited the lowest overpotentials in AORs at 10 mA cm ^−2 , promoting GOR at 224 ± 6 mV lower potential compared to OER. When pyrolysis was conducted at 400 °C, the BO-containing catalyst showed a significant increase in the electrocatalytic activity for the AORs compared to the CoNiB catalyst only. The product selectivity on the different catalysts was investigated in a batch-type reactor with flow recirculation revealing formate as the main oxidation product during GOR and EGOR with faradaic efficiencies (FE) in a range of 60%–80%, while acetate was obtained during EOR (FE ∼ 85%–90%). The electrode potential, electrolyte composition and the type of ionomer were explored with respect to their influence on the GOR selectivity. The use of different ionomers resulted in significant differences in the activity trends between RDE and the batch-type reactor with flow recirculation measurements, indicating a strong influence of the two different substrates used, namely glassy carbon and carbon paper on the catalyst formation and thus on the recorded electrochemical activity

Oxidative depolymerisation of kraft lignin

The production of green hydrogen may be greatly aided by the use of an alternative anode reaction replacing oxygen evolution to increase energy efficiency and concomitantly generate value-added products. Lignin, a major component of plant matter, is accumulated in large amounts in the pulp and paper industry as waste. It has excellent potential as a source of aromatic compounds and can be transformed into the much more valuable aroma chemical vanillin by electrochemical depolymerisation. We used a flow-through model electrolyser to evaluate electrocatalyst-modified Ni foam electrodes prepared by a scalable spray-polymer preparation method for oxidative lignin depolymerisation. We demonstrate how pulsing, i. e. continuously cycling between a lower and a higher applied current, increases the amount of formed vanillin while improving the energy efficiency. Further, we present a scanning droplet cell-assisted high-throughput screening approach to discover suitable catalyst materials for lignin electrooxidation considering that a suitable electrocatalyst should exhibit high activity for lignin depolymerization and simultaneously a low activity for vanillin oxidation and oxygen evolution. Combining electrosynthesis and electrocatalysis can aid in developing new customised materials for electrochemical processes of potential industrial interest

Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia

Electrocatalytic recycling of waste nitrate ($NO_{3}$$^-$) to valuable ammonia ($NH_3$) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate $NH_3$ synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade $NO_{3}$$^-$-to-$NH_3$ conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell $Cu/CuO_x$ and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner $Cu/CuO_x$ phases preferentially catalyze $NO_{3}$$^-$ reduction to $NO_{2}$$^-$, which is rapidly reduced to $NH_3$ at the nearby Co/CoO shell. This unique tandem catalyst system leads to a $NO_{3}$$^-$-to-$NH_3$ Faradaic efficiency of 93.3 $\pm$ 2.1% in a wide range of $NO_{3}$$^-$ concentrations at pH 13, a high $NH_3$ yield rate of 1.17 mmol $cm^{−2} h^{−1}$ in 0.1 M $NO_{3}$$^-$ at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports

Structure‐performance relationship of LaFe1‐xCoxO3LaFe_{1‐x}Co_{x}O_{3} electrocatalysts for oxygen evolution, isopropanol oxidation, and glycerol oxidation

Mitigating high energy costs related to sustainable H2 production via water electrolysis is important to make this process commercially viable. Possible approaches are the investigation of low-cost, highly active oxygen evolution reaction (OER) catalysts and the exploration of alternative anode reactions, such as the electrocatalytic isopropanol oxidation reaction (iPOR) or the glycerol oxidation reaction (GOR), offering the possibility of simultaneously lowering the anodic overpotential and generating value-added products. A suitable class of catalysts are non-noble metal-based perovskites with the general formula $ABO_{3}$, featuring rare-earth metal cations at the A- and transition metals at the B-site. We synthesised a series of $LaFe_{1‐x}Co_{x}O_{3}$ materials with x=0–0.70 by automated co-precipitation at constant pH and subsequent calcination at 800°C. X-ray diffraction studies revealed that the phase purity was preserved in samples with x$\leq$0.3. The activity towards the OER, iPOR, and GOR was investigated by rotating disk electrode voltammetry, showing a relation between structure and metal composition with the activity trends observed for the three reactions. Additionally, GOR product analysis via high-performance liquid chromatography (HPLC) was conducted after 24 and 48 h electrolysis in a circular flow-through cell setup, pointing out a trade-off between activity and selectivity

Aerosol‐based synthesis of multi‐metal electrocatalysts for oxygen evolution and glycerol oxidation

Discovery of new catalysts is crucial for future growth and development of environmentally friendly energy conversion processes e. g. the production of hydrogen by water electrolysis. We developed an aerosol-based synthesis technique as a comparatively fast and facile method to prepare multi-metal catalysts. 22 different quinary metal compositions were synthesized and investigated with respect to their activity for the oxygen evolution (OER) and the glycerol oxidation (GOR) reactions. The impact of the element composition and the homogeneous distribution of the elements in the particles on catalytic performance were evaluated. The highest activity for OER was found for $Co_{20}Cu_{20}Ni_{20}Fe_{20}Zn_{20}$. For GOR, Ag-containing catalysts were the most active, however, in most cases Ag was locally enriched and not homogeneously mixed with the other metals in the particles. Ag-based catalysts outperformed similar compositions containing one or more noble metals. The GOR selectivity of selected catalysts during long-term electrolysis was also investigated and it was shown that varying the catalyst composition via aerosol-based synthesis is a potential way to modulate the GOR selectivity