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One of the main drawbacks of conventional energy storage systems is the possibility of electrolyte leakage due to faulty encapsulation or accidental overcharge. In this work, novel environmentally benign all-biopolymer-based hydrogels have been designed to be used as electrolytes in aqueous electrochemical capacitors. A primary component of gels, i.e. microcrystalline cellulose dissolved in NaOH/urea mixture and cross-linked with epichlorohydrin, was used in combination with agarose, or subsequently introduced agarose and poly(norepinephrine) to form the three-dimensional interpenetrated polymer network of enhanced mechanical stability. The effect of introduced components has been studied independently and investigated in terms of morphology, conductivity, swelling degree, and mechanical/structural properties. The electrochemical diagnostic tests of electrochemical capacitors utilizing acidic (H 2 SO 4 , H 4 SiW 12 O 40) and neutral (Na 2 SO 4) electrolyte-saturated hydrogels of the best overall characteristics have revealed the performance approaching the one characteristic of the liquid electrolyte-based counterparts but with lower self-discharge. The systems were characterized by the capacitance of 97–127 F g−1 at 0.1 A g−1 with retention of 33–89% at 20 A g−1, and cycling life of 10 000 cycles with a maximum of 10% of capacitance loss. The effect of intentionally improved hydrophilic properties of activated carbon electrodes, on the interfacial compatibility between electrode/hydrogel electrolyte is discussed as well. The results are in line with the global trend of green and sustainable energy storage designed for specific applications, i.e. in-vivo systems and wearable electronics. • Novel hydrogels based solely on biopolymers were successfully synthesized. • Poly (norepinephrine) increased the mechanical strength of produced materials. • Materials were deployed as hydrogel electrolytes in electrochemical capacitors. • The electrochemical performance was similar to the conventional liquid-type cells. • Silicotungstic acid as a hydrogel component reveals a superior charge-discharge rate. [ABSTRACT FROM AUTHOR]

The electrochemical reduction reaction of the nitrate ion (NO 3 −), a widespread water pollutant, to valuable ammonia (NH 3) is a promising approach for environmental remediation and green energy conservation. The development of high-performance electrocatalysts to selectively reduce NO 3 − wastes into value-added NH 3 will open up a different route of NO 3 − treatment, and impose both environmental and economic impacts on sustainable NH 3 synthesis. Transition metal phosphides represent one of the most promising earth-abundant catalysts with impressive electrocatalytic activities. Herein, we report for the first time the electrocatalytic reduction of NO 3 − using different phases of iron phosphide. Particularly, FeP and Fe 2 P phases were successfully demonstrated as efficient catalysts for NH 3 generation. Detection of the in-situ formed product was achieved using electrooxidation of NH 3 to nitrogen (N 2) on a Pt electrode. The Fe 2 P catalyst exhibits the highest Faradaic efficiency (96 %) for NH 3 generation with a yield (0.25 mmol h−1 cm-−2 or 2.10 mg h−1 cm−2) at − 0.55 V vs. reversible hydrogen electrode (RHE). The recycling tests confirmed that Fe 2 P and FeP catalysts exhibit excellent stability during the NO 3 − reduction at − 0.37 V vs. RHE. To get relevant information about the reaction mechanisms and the fundamental origins behind the better performance of Fe 2 P, density functional theory (DFT) calculations were performed. These results indicate that the Fe 2 P phase exhibits excellent performance to be deployed as an efficient noble metal-free catalyst for NH 3 generation. [Display omitted] • Iron phosphide films were synthesized for NO 3 − reduction reaction (NO 3 RR) to NH 3. • Detection of the in-situ product was achieved using electrooxidation of NH 3 to N 2. • Fe 2 P film exhibits 96 % Faradaic efficiency for NH 3 generation at − 0.55 V vs RHE. • Recycling test showed that FeP electrocatalyst is stable during the NO 3 RR. • DFT (RPBE+D3 level) in an aqueous solution was used to study the NO 3 RR mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Different approaches to enhancement of electrocatalytic activity of noble metal nanoparticles during oxidation of small organic molecules (namely potential fuels for low-temperature fuel cells such as methanol, ethanol and formic acid) are described. A physical approach to the increase of activity of catalytic nanoparticles (e.g. platinum or palladium) involves nanostructuring to obtain highly dispersed systems of high surface area. Recently, the feasibility of enhancing activity of noble metal systems through the formation of bimetallic (e.g. PtRu, PtSn, and PdAu) or even more complex (e.g. PtRuW, PtRuSn) alloys has been demonstrated. In addition to possible changes in the electronic properties of alloys, specific interactions between metals as well as chemical reactivity of the added components have been postulated. We address and emphasize here the possibility of utilization of noble metal and alloyed nanoparticles supported on robust but reactive high surface area metal oxides (e.g. WO3, MoO3, TiO2, ZrO2, V2O5, and CeO2) in oxidative electrocatalysis. This paper concerns the way in which certain inorganic oxides and oxo species can act effectively as supports for noble metal nanoparticles or their alloys during electrocatalytic oxidation of hydrogen and representative organic fuels. Among important issues are possible changes in the morphology and dispersion, as well as specific interactions leading to the improved chemisorptive and catalytic properties in addition to the feasibility of long time operation of the discussed systems. [Copyright &y& Elsevier]

Abstract: A novel Pd electrocatalyst is developed by self-assembly of Pd nanopartilces on phosphomolybdic acid (HPMo)-poly(diallyldimethylammonium chloride) (PDDA)-functionalized multiwalled carbon nanotubes supports (Pd/HPMo-PDDA-MWCNTs). The as-synthesized Pd/HPMo-PDDA-MWCNTs were characterized by TEM, EDS mapping, Raman spectra, X-ray photoelectron spectroscopy, electrochmeical CO stripping and cyclic voltammetry techniques. Pd nnaoparticles deposited on HPMo-PDDA-MWCNTs are in the range of 3.1 nm with uniform distributon. Pd/HPMo-PDDA-MWCNT catalysts have lower overpotential for COad oxidation manifested as lower peak and onset potentials as compared to acid-treated MWCNTs supported Pd (Pd/AO-MWCNTs) and carbon supported Pd catalysts (Pd/C). Pd/HPMo-PDDA-MWCNTs catalysts also exhibit a much higher electrocatalytic activity and stability for formic acid oxidation reaction as compared to that on Pd/AO-MWCNTs and Pd/C. The high electrocatalytic activities of Pd/HPMo-PDDA-MWCNTs catalysts are most likely related to highly dispersed and fine Pd nanoparticles as well as synergistic effects between Pd and HPMo immobilized on PDDA-functionalized MWCNTs. [Copyright &y& Elsevier]

Abstract: RuSe x electrocatalytic nanoparticles were deposited onto hybrid carriers composed of Black Pearl carbon-supported tungsten oxide; and the resulting system''s electrochemical activity was investigated during oxygen reduction reaction. The tungsten oxide-utilizing and RuSe x nanoparticle-containing materials were characterized using transmission electron microscopy, X-ray diffraction and electrochemical diagnostic techniques such as cyclic voltammetry and rotating ring-disk voltammetry. Application of Black Pearl carbon carriers modified with ultra-thin films of WO3 as matrices (supports) for RuSe x catalytic centers results during electroreduction of oxygen in 0.5moldm−3 H2SO4 (under rotating disk voltammetric conditions) in the potential shift of ca. 70mV towards more positive values relative to the behavior of the analogous WO3-free system. Also the percent formation (at ring in the rotating ring-disk voltammetry) of the undesirable hydrogen peroxide has been decreased approximately twice by utilizing WO3-modified carbon carriers. The results are consistent with the bifunctional mechanism in which oxygen reduction is initiated at RuSe x centers and the hydrogen peroxide intermediate is reductively decomposed at reactive WO3-modified Black Pearl supports. The electrocatalytic activity of the system utilizing WO3-modified Black Pearl supports has been basically unchanged upon addition of acetic acid, formic acid or methyl formate to the sulfuric acid supporting electrolyte. [Copyright &y& Elsevier]

Abstract: We propose a novel composite (hybrid) organic/inorganic system that can be prepared as a coating (on 1μm level) on glassy carbon and metal electrode substrates. Poly(3,4-ethylenedioxythiophene) or PEDOT based composite coatings were electrodeposited using cyclic voltammetry on glassy carbon and stainless steel substrates in the presence of 4-(pyrrole-1-yl) benzoic acid (PyBA) and phosphododecamolybdic acid (PMo12). The coating growth was facilitated by the addition of polyoxyethylene-10-laurylether (BRIJ10) neutral surfactant at the level of 0.04moldm−1 to improve solubility of the 3,4-ethylenedioxythiophene monomer and to form an aqueous micellear solution in the reaction medium. The fact that carboxylate-containing PyBA units link positively charged PEDOT structures tends to improve overall stability and adherence of composite coatings to stainless steel. The PEDOT/PyBA composite serves as a stable host matrix for large negatively charged polymolybdate inorganic species. Consequently, due to the formation of denser polymeric structures and to the existence of electrostatic repulsion effects, the polyanion-containing composite coatings are capable of largely blocking the access of pitting-causing anions (chlorides) to the surface of stainless steel. Interaction of phosphomolybdate with metal ions, namely with chromium(III) or even iron(III) or iron(II) that exist at the stainless steel–composite coating interface, may lead to the formation of insoluble deposits and exhibit overall passivating effect. [Copyright &y& Elsevier]

Abstract: Scanning electrochemical microscopy (SECM) in the feedback mode was utilized for monitoring the surface reactivity and the localized corrosion processes occurring on the Nd13.5Fe79.5Si1B6 permanent magnet (intrinsically comprising iron inclusions). SECM imaging experiments, performed with the application of ferrocenecarboxylic acid as the mediator, revealed distinctly reactive areas at the magnet surface during early stages of its immersion in 0.1moldm−3 phosphate buffer (pH=7). It was demonstrated that the iron inclusions were responsible for the existence of these reactive areas whereas the bulk material surface was practically unreactive (insulating). It was observed that the surface reactivity of the iron inclusions gradually decreased with time and after 7h immersion the whole magnet surface became uniformly unreactive (insulating). The results were explained in terms of differences in the dynamics of the passive film formation on the iron inclusions and on the bulk material. Another factor that might be responsible for the observed non-uniform surface reactivity was also considered, namely, the differences in abilities to charge propagation through passive films existing on the iron inclusions and on the bulk material. The role of the iron inclusions as pitting precursor sites in the presence of chlorides in the phosphate buffer solution was also examined. [Copyright &y& Elsevier]

Abstract: Combination of multi-walled carbon nanotubes, cobalt porphyrin and tungsten oxide in the film (deposited onto glassy carbon electrode substrate) produces an electrocatalytic system capable of effective reduction of oxygen in such acid medium as 0.5moldm−3 H2SO4. Co-existence of cobalt porphyrin and tungsten oxide, together with dispersed carbon nanotubes, leads to the enhancement effect evident from some positive shift in the oxygen reduction voltammetric potential and the significant increase of voltammetric currents (relative to those characteristic of the system free of carbon nanotubes and WO3). The multi-component electrocatalytic film has also exhibited relatively higher activity towards reduction of hydrogen peroxide. It is reasonable to expect that the reduction of oxygen is initiated at the cobalt porphyrin redox centers, and the undesirable hydrogen peroxide intermediate is further reduced at the tungsten oxide support. An important function of carbon nanotubes is to improve transport of electrons within the electrocatalytic multi-component film. [Copyright &y& Elsevier]

Abstract: Modification of carbon-supported RuSe x nanoparticles with ultra-thin WO3 films results in the enhancement of their electrocatalytic properties towards electroreduction of dioxygen in acid medium (0.5moldm−3 H2SO4) as evidenced from the positive shift of the O2 reduction potential (ca. 150mV) and the higher heterogeneous rate constant (ca. 3 times). An important issue is that the mixed-valent tungsten(VI,V) oxide support is characterized by good electronic and protonic conductivities. Further, not only RuSe x is catalytic but tungsten oxide itself is also capable of promoting the reduction of hydrogen peroxide. This bifunctional activity of the WO3-modified system has been the most pronounced at rather low loadings (e.g. 80μgcm−2) of RuSe x nanoparticles. To facilitate attachment of catalytic particles to glassy carbon substrate, they have been over-coated with Nafion. [Copyright &y& Elsevier]