Gumaa A. El-Nagar

Novel fuel blends facilitating the electro-oxidation of formic acid at a nano-Pt/GC electrode

This paper addresses the promoting effect of the electrooxidation of formic acid (FAO) at a nano-Pt/GC electrode in the presence of selected low molecular weight alcohols (R–OH) as blending components. That is, blending FA with different molar ratios of methanol (MeOH), ethanol (EtOH), ethylene glycol (EGOH) and isopropanol (PrOH) resulted in a significant enhancement of the direct FAO to CO2 (desired pathway) with a concurrent depression of the amount of CO produced from the “non-faradaic” dissociation of FA. Moreover, a favorable negative shift of the onset potential of the direct FAO peak at the nano-Pt/GC electrode is observed. Fuel utilization (FU = amount of charge consumed during the oxidation process per mole of fuel) and the turnover number (TON = number of FA molecules oxidized per platinum site per second) are significantly enhanced as well for FAO in the various FA/R–OH blends compared to pure FA. That is, the use of equimolar amounts of FA with either EtOH, MeOH, EGOH or PrOH resulted in a facile FAO at the nano-Pt/GC electrode of about 9, 7, 5 and 4 times higher FU compared to pure FA, respectively. Similar increase of TON is observed as well. The blending component is believed to adsorb at the Pt surface sites and thus disfavor the “non-faradaic” dissociation of FA to CO. Additionally; it might induce the CH-down adsorption orientation of FA, thus favoring FAO to CO2. The enhanced oxidation activity indicates that this fuel blend is a promising fuel system.

Efficient 3D-Silver Flower-like Microstructures for Non-Enzymatic Hydrogen Peroxide (H2O2) Amperometric Detection

We present an efficient non-enzymatic hydrogen peroxide sensor composed of flower-like silver microstructures. The silver microstructures´ morphology is controlled by adding minute amounts of either succinic or malonic acid as directing agents. Morphologically, silver particles showed ball-like structures in the absence of both directing agents, while the presence of 50 ppm of succinic acid and malonic acid lead to monodisperse chrysanthemum and water-lily flower-like structure, respectively. A higher concentration of succinic acid resulted in a rose flower-like structures. Electrochemically, the rose flower-like silver microstructures exhibited the best performance for H2O2 detection as evaluated by their outstanding electrocatalytic activity (12 times higher) and sensitivity (2.4 mM−1 cm−2, 24 times higher) with lower detection limit (0.4 µM, 5 times smaller) together with their excellent H2O2 selectivity compared to that of the ball-shaped structures. Additionally, rose-flower microstructures exhibited excellent long-term stability; 11 and 3 times higher compared to ball- and water-lily structures, respectively. This substantial performance enhancement is attributed to their unique flower-like structure providing a higher number of active surface sites (at least 8 times higher) and a faster detachment rate of in-situ generated oxygen bubbles from their surface.

Electrocatalysis of Formic Acid Electro-Oxidation at Platinum Nanoparticles Modified Surfaces with Nickel and Cobalt Oxides Nanostructures

The present study proposes a novel promising binary catalyst for formic acid electro-oxidation (FAO); the main anodic reaction in direct formic acid fuel cells (DFAFCs). The catalyst is basically composed of two metal oxides of nickel and cobalt nanostructures (i.e., NiOx and CoOx) assembled onto a platinum nanoparticles (PtNPs)−modified glassy carbon (Pt/GC) electrode. Actually, FAO proceeds at bare Pt surfaces in two parallel routes; one of them is desirable (called direct or hydrogenation) and occurred at a low potential domain (I p d ). While, the other (undesirable) involves the dehydration of formic acid (FA) at low potential domain to produce a poisoning intermediate (CO), which next be oxidized (indirect, I p ind ) at a higher potential domain after the platinum surface becomes hydroxylated. Unfortunately, the peak current ratio (I p d /I p ind ) of the two oxidation routes, which monitors the degree of the catalytic enhancement and the poisoning level, stands for bare Pt surfaces at a low value (less than 0.2). Interestingly, this ratio increased significantly as a result of the further modification of the Pt/GC electrode with NiOx \( \left({I}_{\mathrm{p}}^{\mathrm{d}}/{I}_{\mathrm{p}}^{\mathrm{ind}}=3\right) \), CoOx \( \left({I}_{\mathrm{p}}^{\mathrm{d}}/{I}_{\mathrm{p}}^{\mathrm{ind}}=4\right) \) and a binary mixture of both \( \left({I}_{\mathrm{p}}^{\mathrm{d}}/{I}_{\mathrm{p}}^{\mathrm{ind}}=15\right) \). This highlights the essential role of these in promoting the direct FAO, presumably via a mediation process that ultimately improved the oxidation kinetics or through a catalytic enhancement for the oxidation of the poisoning CO at the low potential domain of the direct FAO. The effect of the deposition order of NiOx and CoOx on the catalytic activity was addressed and fount influencing. The addition of CoOx to the catalyst was really important, particularly in improving the catalytic stability of the catalyst towards a long-term continuous electrolysis experiment, which actually imitates the real industrial applications.

Electro-Oxidation of Formic Acid, Glucose, and Methanol at Nickel Oxide Nanoparticle Modified Platinum Electrodes

The current study presents a comparison for the electro-oxidation of formic acid (FA), glucose (GL), and methanol (ME) at nickel oxide nanoparticles (NiOx) modified electrodes. The modification with NiOx was pursed onto a bare glassy carbon (GC) and Pt-modified (Pt/GC) electrodes electrochemically, and the catalytic activity was measured in 0.3 M NaOH. Cyclic voltammetry (CV), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) are all used to provide a concrete characterization of the prepared electrodes. A catalytic enhancement of GL oxidation (GLO) and ME oxidation (MEO) was observed at the NiOx-modified GC (NiOx/GC) electrode, while the same electrode did not show any activity towards FA oxidation (FAO), revealing that FAO is substrate dependent. On the other hand, assembling NiOx onto the Pt/GC electrode assisted in improving the catalytic activity of all reactions (GLO, MEO, and FAO). The catalytic enhancement observed at the NiOx/Pt/GC electrode for GLO, MEO, and FAO was not only confined in the large increase of the oxidation current but also in a negative shift in the onset potential of the oxidation reaction. We believe NiOx could successfully play an essential role in this catalytic enhancement, presumably via participation in these reactions in a way facilitating the charge transfer or providing the oxygen atmosphere necessary for promoting an oxidative removal for unwanted poisoning species.

The Origin of Electrocatalytic Activity of Gold Nanoparticles Modified Pt-Based Surfaces Towards Formic Acid Oxidation

Recently, direct formic acid fuel cells (DFAFCs) have received much attention in both industry and academia, due to their unique properties. Despite of their broad benefits, DFAFCs have two major drawbacks that limit its lifetime and efficiency; the poor electrocatalytic activity (due to CO and Halides poisoning) and stability of the Pt-based electrodes. Herein, the electrocatalytic activity, stability and tolerance against poisoning species (CO and Halides) of Pt-based electrode (Pt/GC) towards formic acid (FA) oxidation; essential anodic reaction of DFAFCs, are shown to increase via interrupting the Pt surface with gold nanoparticles (AuNPs). Electrochemical measurements show that gold nanopartciles (AuNPs) modified Pt/GC (Au/Pt/GC) electrode supports a significant enhancement on the direct FA oxidation to CO2 (the dehydrogenation pathway). On the other hand, the oxidative treatment of GC (GCox) in acidic medium results in 2 times increases on the catalytic activity of unmodified and AuNPs modified Pt electrodes towards direct FA oxidation to CO2 compared to un-oxidized GC electrode. This significantly enhanced activity of AuNPs modified Pt/GC catalysts can be attributed to noncontiguous arrangement of Pt sites in the presence of the neighbored AuNPs, which promotes direct oxidation of FA to CO2 and retards the adsorption of CO at Pt surface. Moreover, AuNPs modified Pt/GC catalyst has satisfactory stability and show high tolerance against halides poisoning.

Electrocatalytic Activity of NiOx Nanostructured Modified Electrodes Towards Oxidation of Small Organic Molecules

Nickel oxide nanostructured modified platinum nanoparticles (PtNPs) supported in glassy carbon electrode (NiOx/Pt/GC) was used as an effective anode for formic acid (FA), methanol (ME) and ethanol (ET) electrooxidation in 0.3 M NaOH solution. GC surface was fabricated with NiOx nanostructured and Pt nanoparticles electrochemically. The modified electrodes were characterized using cyclic voltammetry (CV) and scanning electron microscopy (SEM). The catalytic improvement observed at NiOx/Pt/GC electrode for FAO, MEO, and ETO was not only confined in the large increase of the oxidation current but also in a negative shift in the onset potential of the oxidation reactions. The influence of temperature on the oxidation current was investigated and the apparent activation energy, E a , for each fuel was calculated at a specific potential. Furthermore, NiOx/Pt/GC electrode showed a satisfactory stability for FAO, MEO, and ETO in 0.3 M NaOH solution.