We present the synthesis and characterization of two monometallic coordination polymers, Co(L)
2
(H
2
O)
2
n
(
Co-CP
) and Ni(L)
2
(H
2
O)
2
n
(
Ni-CP
), alongside a heterobimetallic counterpart,
...CoNi-CP
, derived from an amide-based multifunctional pro-ligand 4-(pyrimidin-5-ylcarbamoyl)benzoic acid (HL), and discussed their electrocatalytic activity in the oxygen evolution reaction (OER). The CPs were characterized using various techniques, including elemental analysis, IR spectroscopy, X-ray diffraction, and thermal and powder XRD analyses. The low-cost amide-functionalized transition metal pristine coordination polymers
Co-CP
and
Ni-CP
were demonstrated to catalyze the OER in alkaline media, surpassing the benchmark IrO
2
electrocatalyst performance. The heterometallic coordination polymer (
CoNi-CP
) displayed a lower Tafel slope value (and thus, faster kinetics) and higher long-term durability compared to its monometallic counterparts,
Co-CP
and
Ni-CP
. The results obtained show a pristine transition metal heterobimetallic coordination polymer as a low-cost electrocatalyst of great promise and high performance for OER catalysis in alkaline media.
Pristine multifunctional amide-based bimetallic Co-Ni coordination polymer and monometallic counterparts as efficient electrocatalysts for the oxygen evolution reaction.
PtAu nanoparticles spontaneously deposited on graphene support, PtAu/rGO, have shown remarkably high catalytic activity for hydrogen evolution reaction (HER) in sulfuric acid solution. SEM images of ...the PtAu/rGO electrode surface showed that Pt nanoparticles that are non-uniform in size occupy both the edges of previously deposited uniform Au nanoparticles and the edges of graphene support. XPS analysis showed that the atomic percentages of Au and Pt in PtAu/rGO were 0.6% and 0.3%, respectively. The atomic percentage of Au alone on previously prepared Au/rGO was 0.7%. Outstanding HER activity was achieved for the PtAu/rGO electrode, showing the initial potential close to the equilibrium potential for HER and a low Tafel slope of −38 mV/dec. This was confirmed by electrochemical impedance spectroscopy. The chronoamperometric measurement performed for 40 min for hydrogen evolution at a constant potential indicated good stability and durability of the PtAu/rGO electrode.
This paper presents a comparative analysis of three carbon-based electrodes: bare multiwalled carbon nanotubes (MWCNT), SnO2/MWCNT, and PbO2/graphene-nanoribbons (PbO2/GNR) composites, as anodes for ...the electrooxidative degradation of Rhodamine B as a model organic pollutant. Anodic electrooxidation of Rhodamine B was performed on all three electrodes, and the decolorization efficiency was found to increase in the order MWCNT < PbO2/GNR < SnO2/MWCNT. The electrodes were characterized by X-ray photoelectron spectroscopy (XPS) and linear sweep voltammetry (LSV). It was proposed that, in the 0.1 M Na2SO4 applied as electrolyte, observed decolorization mainly occurs in the interaction of Rhodamine B with OH radical adsorbed on the anode. Finally, the obtained results were complemented with Density Functional Theory (DFT) calculations of OH-radical interaction with appropriate model surfaces: graphene(0001), SnO2(001), and PbO2(001). It was found that the stabilization of adsorbed OH-radical on metal oxide spots (SnO2 or PbO2) compared to carbon is responsible for the improved efficiency of composites in the degradation of Rhodamine B. The observed ability of metal oxides to improve the electrooxidative potential of carbon towards organic compounds can be useful in the future design of appropriate anodes.
Hydrogen evolution reaction (HER) was investigated on reduced graphene oxide (rGO)-supported Au and PdAu nanoparticles in acid solution. The graphene spread over glassy carbon (rGO/GC) was used as a ...support for the spontaneous deposition of Au and Pd. The resulting Au/rGO and PdAu/rGO electrodes were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) techniques. Phase AFM images have shown that the edges of the rGO sheets were active sites for the deposition of both Au and Pd. XPS analysis revealed that the atomic percentages of both Au and PdAu nanoparticles were slightly higher than 1%. The activity of the PdAu/rGO electrode for the HER was remarkably high, with the overpotential close to zero. HER activity was stable over a 3 h testing time, with a low Tafel slope of approx. −46 mV/dec achieved after prolonged hydrogen evolution at a constant potential.
PdPt bimetallic nanoparticles on carbon-based supports functioning as advanced electrode materials have attracted attention due to their low content of noble metals and high catalytic activity for ...fuel cell reactions. Glassy carbon (GC)-supported Pt and PdPt nanoparticles, as promising catalysts for the oxygen reduction reaction (ORR), were prepared by the electrochemical deposition of Pt and the subsequent spontaneous deposition of Pd. The obtained electrodes were examined using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), and electroanalytical techniques. An XPS analysis of the PdPt/GC with the highest ORR performance revealed that the stoichiometric ratio of Pd: Pt was 1:2, and that both Pt and Pd were partially oxidized. AFM images of PdPt2/GC showed the full coverage of GC with PdPt nanoparticles with sizes from 100–300 nm. The ORR activity of PdPt2/GC in an acid solution approached that of polycrystalline Pt (E1/2 = 0.825 V vs. RHE), while exceeding it in an alkaline solution (E1/2 = 0.841 V vs. RHE). The origin of the improved ORR on PdPt2/GC in an alkaline solution is ascribed to the presence of a higher amount of adsorbed OH species originating from both PtOH and PdOH that facilitated the 4e-reaction pathway.
The present work was focused on doping of 1% and 5% both of Nd2O3 and Sm2O3 in geopolymer gels. One of the main goals was to determine the influence of the behavior of Nd and Sm as dopants and ...structural nanoparticles changes of the final geopolymer formed. It is shown that the disorder formed by alkali activation of metakaolin can accommodate the rare earth cations Nd3+ and Sm3+ into their aluminosilicate framework structure. The main geopolymerization product identified in gels is Al-rich (Na)-AS-H gel comprising Al and Si in tetrahedral coordination. Na+ ions were balancing the negative charge resulting from Al3+ in tetrahedral coordination. The changes in the structures of the final product (geopolymer/Nd2O3; Sm2O3), has been characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analysis with energy dispersive spectrometry (EDS). Nucleation at the seed surfaces leads to the formation of phase-separated gels from rare earth phase early in the reaction process. It is confirmed that Nd and Sm have been shown to form unstable hydroxides Nd(OH)3 and Sm(OH)3 that are in equilibrium with the corresponding oxides.
Sn-Pd electrocatalysts with a constant atomic ratio of 60 at.% Sn-40 at.% Pd suitable for potential application in direct ethanol fuel cells were synthesized using a novel two-step electrodeposition ...method. First, Sn was electrodeposited in various forms of dendrites, from spear-like and needle-like to individual fern-like dendrites to a network of intertwined fern-like dendrites, by varying the cathodic potential and then performing electrodeposition of Pd at a constant current density in the second step. A morphological and elemental analysis of Sn and Sn-Pd electrocatalysts was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques, while the size of Sn dendrites was analyzed using the particle size distribution (PSD) method. Cyclic voltammetry (CV) and chronoamperometry were applied in order to study the catalytic behavior of Sn-Pd electrocatalysts in the ethanol oxidation reaction (EOR), while CO stripping was used to estimate the antipoisoning capability of the electrocatalysts. The Sn surface morphology of the sub-layer was highly correlated with the electrocatalytic activity of the examined Sn-Pd electrocatalysts. The high activity it presented towards the EOR showed the suitability of the Sn-Pd electrocatalyst constructed from individual fern-like Sn dendrites as a sub-layer. Compared to Pd alone, this Sn-Pd catalyst showed more than 3 times higher activity and improved EOR kinetics. This enhancement in the catalytic activity of the Sn-Pd electrocatalysts is attributed to both the morphological characteristics of Sn as a sub-layer and the bifunctional effect.
HER was examined on various glassy carbon-supported Au and PdAu electrodes in acid solution. The Au/GC electrodes were obtained after Au was electrodeposited on a GC substrate by holding the ...potential for various times in 0.5 M H2SO4 solution containing AuCl4− ions. PdAu/GC electrodes were obtained after Pd has been added by a spontaneous deposition on previously prepared Au/GC electrodes. Surface morphology and chemical analysis of Au/GC and PdAu/GC electrodes were performed by atomic force microscopy and X-ray photoemission spectroscopy. Electrochemical characterization was performed by cyclic voltammetry in 0.5 M H2SO4 solution, while the linear sweep voltammetry was used to gain insight into the electrocatalytic activity of these electrodes for HER. 30minPd/10minAu/GC electrode consisting of 48% Pd and 65% Au, with the total coverage of the GC substrate with PdAu islands of 70%, showed the best catalytic activity for HER. A remarkable high activity and stability of this electrode makes it a promising catalyst for HER in acid solution.
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•Au/GC was prepared by the electrochemical deposition of Au on GC.•Pd nanoislands were deposited spontaneously on Au/GC.•AFM and XPS were used for Au/GC and PdAu/GC surface characterization.•Activity of Au/GC for HER exceeds that of Au (111) in acid solution.•PdAu/GC activity for HER exceeds the activity of a corresponding Pd/Au (111).
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•FeNi/rGO showed two times higher OER current density than the IrO2 electrocatalyst.•FeNi/rGO gave η10 lower for 100 mV compared to IrO2 electrocatalyst during OER.•All three FeM/rGO ...electrocatalysts showed comparable ORR catalytic activity.•Good stability of FeM/rGO electrocatalysts during ORR was noticed.
Three different iron-based electrocatalysts deposited on reduced graphene oxide (Fe/rGO, FeNi/rGO, and FeCu/rGO) were synthesized and examined for oxygen reduction and evolution reactions (ORR and OER, respectively) in alkaline media. X-ray powder diffraction analysis, Fourier transform infrared spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy were used for a thorough investigation of physico-chemical properties of FeM/rGO electrocatalysts. XPS analysis indicated the presence of transition metals in higher oxidation states. Onset potentials during OER were found to be 1.51, 1.64, and 1.71 V for FeNi/rGO, FeCu/rGO, and Fe/rGO, respectively. Moreover, FeNi/rGO showed the highest OER current density (∼40 mA cm−2 at 2 V), two times higher than the benchmark OER electrocatalyst, IrO2, and the lowest Tafel slope (88 mV dec-1), lower than IrO2. The somewhat better catalytic activity of Fe/rGO for ORR in alkaline media compared to FeNi/rGO and FeCu/rGO was noticed. Tafel slopes of 105, 112, and 113 mV dec-1 during ORR were found for Fe/rGO, FeCu/rGO, and FeNi/rGO, respectively. Almost constant ORR current densities during chronoamperometric measurements were noticed for Fe/rGO and FeCu/rGO indicating stable performance.
Porous cobalt (III) oxide (Co3O4) and mixed cobalt (III) oxide - tin oxide (Co3O4/SnO2) were prepared by a novel template-based hydrothermal method resulting in their spherical morphology as ...confirmed by thorough physico-chemical characterisation. Two oxides were systematically examined as bifunctional electrocatalysts for oxygen reduction (ORR) and evolution (OER) reaction in alkaline media by voltammetry with rotating disk electrode, electrochemical impedance spectroscopy, and chronoamperometry. Low-cost Co3O4 and Co3O4/SnO2 electrocatalysts showed excellent ORR performance with low onset and half-wave potential, low Tafel slope, and the number of exchange electrons near 4, comparable to the commercial Pt/C electrocatalyst. Low OER onset potential of 1.52 and 1.57 V was observed for Co3O4 and Co3O4/SnO2, respectively, with low charge transfer resistance under anodic polarization conditions. Finally, to test bifunctional activity and durability of the two electrocatalyst, switch OER/ORR test was carried out.
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•Spherical Co3O4 and Co3O4/SnO2 were synthesized by the hydrothermal method.•Both electrocatalysts showed excellent ORR performance comparable with Pt/C.•OER at Co3O4 electrocatalyst starts ca. 50 mV earlier than at Co3O4/SnO2.•Co3O4/SnO2 gave comparable OER current densities to Co3O4.•Co3O4 and Co3O4/SnO2 could be promising candidates for metal-air batteries.
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