Strain-driven adsorption site modification on Pd-based nano cube for fuel cell application

BackgroundCobalt oxide (Co3O4) is a promising electrocatalyst for efficient urea electro-oxidation, tackling power consumption and environmental challenges. The controllable design of free-standing Co3O4 nanostructures grown on Ni foam (NF) substrates was achieved using a green and facile hydrothermal approach. Different reducing agents were applied to synthesize various morphological structures of Co3O4, including nanoparticles, nanowires, and nanocubes (NCs) morphologies.ResultsThe as-fabricated electrodes were investigated as electrocatalysts for enhanced urea electro-oxidation. Because of its 3D nanostructure with minimal agglomeration and a large interfacial surface area with adequate electroactive sites, the Co3O4 NCs/NF had the best energy conversion efficiency of any electrode toward the urea oxidation process. These distinctive features facilitated the electron and urea routes used in the urea electro-oxidation process. It had a low-onset potential of 194.2 mV (vs. Hg/HgO) and a current density of 90.2 mA cm−2 in a 1 M KOH electrolyte. The electrocatalyst demonstrated excellent anodic activity for urea electro-oxidation with an onset potential of 196.7 mV and a current density of 256.1 mA cm−2 in 1 M KOH + 0.3 M urea concentration. Furthermore, the Co3O4 NCs/NF exhibited long-term stability, as shown by chronoamperometry and stepwise tests after 3600 s in the presence of urea under various operating conditions.ConclusionsCompared to all the fabricated Co3O4 nanostructures, the Co3O4 nanocubes revealed the highest electrocatalytic performance toward urea electro-oxidation in all concentrations. Therefore, Co3O4 NCs/NF is a promising, robust, and efficient electrocatalyst for direct urea fuel cell applications.

Selective detection of gold(III) ions based on codoped MnO2–SnO2 nanocubes prepared by solution method

Theformic acid oxidation reaction (FAOR) is one of the key reactionsthat can be used at the anode of low-temperature liquid fuel cells.To allow the knowledge-driven development of improved catalysts, itis necessary to deeply understand the fundamental aspects of the FAOR,which can be ideally achieved by investigating highly active modelcatalysts. Here, we studied SnO2-decorated Pd nanocubes(NCs) exhibiting excellent electrocatalytic performance for formicacid oxidation in acidic medium with a SnO2 promotion thatboosts the catalytic activity by a factor of 5.8, compared to purePd NCs, exhibiting values of 2.46 A mg–1Pd for SnO2@Pd NCs versus 0.42 A mg–1Pd for the Pd NCs and a 100 mV lower peak potential. By usingex situ, quasi in situ, and operando spectroscopic and microscopicmethods (namely, transmission electron microscopy, X-ray photoelectronspectroscopy, and X-ray absorption fine-structure spectroscopy), weidentified that the initially well-defined SnO2-decoratedPd nanocubes maintain their structure and composition throughout FAOR.In situ Fourier-transformed infrared spectroscopy revealed a weakerCO adsorption site in the case of the SnO2-decorated PdNCs, compared to the monometallic Pd NCs, enabling a bifunctionalreaction mechanism. Therein, SnO2 provides oxygen speciesto the Pd surface at low overpotentials, promoting the oxidation ofthe poisoning CO intermediate and, thus, improving the catalytic performanceof Pd. Our SnOx-decorated Pd nanocubesallowed deeper insight into the mechanism of FAOR and hold promisefor possible applications in direct formic acid fuel cells.

Dye-sensitized solar cells (DSSCs) have been expected as low-cost, lightweight, and flexible energy conversion devices. To date, the highest conversion efficiency above 12 % has been achieved with p-conjugated macrocyclic zinc porphyrin sensitizer YD2-o-C8 using cobalt polypyridine redox shuttles. Designed p-conjugated macrocycles such as porphyrins and phthalocyanines have attracted special attention as versatile molecular platforms of highly efficient dyes for DSSCs. While a lot of porphyrin-based sensitizers have been designed and synthesized to enhance the conversion efficiency in DSSCs, the efficiencies of DSSCs employing red/near-IR absorbing phthalocyanine-based sensitizers had not been impressive due to their strong tendency to aggregate and the lack of directionality of electron transfer in the excited states. To overcome these drawbacks of phthalocyanine-based sensitizers, several approaches such as steric suppression of aggregation, electronic push-pull structures through asymmetrical substitutions, and optimization of adsorption sites have been reported. Recently, we showed that the structural modification of peripheral bulky substituents and adsorption site around the phthalocyanine core induced the improvement of incident photon-to-current efficiency (IPCE), and thereby achieved a solar-to-electric power-conversion efficiency (PCE) of 5.9% from solar cells employing PcS18 under one sun condition. However, while the maximum value of IPCE was more than 80 %, the values around 520 nm was about 30 %. Since the absorption coefficient of the sensitizers at the wavelength is very low, in order to increase the efficiency, higher dye adsorption density is desired. This can be done by decreasing the molecular size. In addition to IPCE spectrum, open circuit voltage of the PcS18 cell was not high. This could be improved by modifying the size of peripheral substituents attached to the phthalocyanine core to cover the TiO2 surface by the dye molecules. In this presentation, we examine the effect of the length and number of alkoxy groups around the phthalocyanine moiety on the photovoltaic properties. We now expect the alkoxy groups to have three functions, preventing aggregation, filling the space among dyes on TiO2 surface and increasing dye adsorption density. We found that an asymmetrical zinc phthalocyanine (ZnPc) PcS20 bearing propoxy groups in the 2 and 6 positions of peripheral phenoxy units showed a record PCE value of 6.4 % under simulated air mass 1.5 global sunlight.

We present an extensive density functional theory analysis of the structural, electronic, and magnetic properties of isolated $3d$ transition metal adatoms (from Ti to Co) adsorbed on free-standing and Ni(111)-supported graphene. We discuss how the energetics of different adsorption sites is influenced by the filling of $d$-orbital filling across the $3d$ series and identify a direct correlation between the adatom-graphene distance and the degree of charge transfer. The presence of the Ni substrate is found to have stronger impact on the adatoms at the end of the series, leading to modifications of the preferred adsorption site, charge transfer, and spin properties. The magnetic exchange coupling between the spin of the adatom and the Ni magnetization changes as a function of the adatom both in sign (preferred antiferromagnetic exchange for Ti, V, and Cr, and ferromagnetic alignment for the other elements) and in magnitude (from 90 meV for Mn to $\ensuremath{\approx}10$ meV for Fe an Co).

Co-adsorption of multi-components in ZrCo-based hydrogen storage materials can lead to a number of synergistic effects, such as the modification of adsorption sites, and further worsen the hydrogen storage capability. In this work, we explore the co-adsorption of H and CO on the ZrCo(110) surface and find that the molecular CO can be adsorbed on the clean alloy surface and thus decrease the hydrogen storage ability of the alloy. Moreover, CO occupies the adsorption site of H and therefore prevents the adsorption and diffusion into the interior of the lattice. Fortunately, the Hf dopant reduces the number of adsorption sites of the CO molecule and inhibits the formation of carbides to a certain extent. In addition, the partial density of states (PDOS) result shows that there is almost no interaction between the s orbital of H and the s orbital of Co on the pure surface of pre-adsorbed CO, while on the Hf-doped surface of pre-adsorbed CO, the s orbital of H overlapped greatly with the s orbital of Co, indicating that Hf doping inhibits CO toxicity in the interaction between H and the surface. Hence, the doping of Hf has the effect of giving resistance to CO toxicity and is conducive to the adsorption of H.

The DMFC commercialization and practical operations are still confronts several major challenges particularly in high cost, maintaining long-term stability and durability, deteriorating of anode electrocatalyst performance as well as the sluggish methanol oxidation kinetic reaction occurred at the anode due to the poisoning effect of the platinum (Pt) electrocatalyst. The selection of the appropriate anode electrocatalysts for methanol oxidation reaction (MOR) is quite limited, only the anode electrocatalysts that can enhance the MOR activity and minimize the poisoning effect by the carbonaceous intermediate species-like carbon monoxide (CO) can be considered to improve the DMFC performance. The strategy of coupling or alloying Pt with other noble or non-noble metals can prevent such mentioned problems above and able to upgrade the ability of anti-CO poisoning through the modification of the CO adsorption site. In general, the highly accessible of electrocatalytic active sites and dispersed are very important for the superior Pt-based alloy electrocatalyst performance through the utilization of the electrocatalyst support with the large specific surface areas. However, the commonly used carbon supporting materials for monometallic Pt and bimetallic Pt-based alloy electrocatalysts suffer from severe corrosion due to the electrooxidation on the surface under acidic condition at high operating voltages for prolonged times which resulting the dissolution, aggregation, migration and detachment of Pt NPs leading to a serious problem of stability. The most efficient strategy to overcome the limitations described above is through the embedding the monometallic Pt and bimetallic Pt-based alloy electrocatalyst on the metal oxides. This proposed strategy provides a medium to anchor the Pt-based alloy electrocatalyst securely onto the carbonaceous support materials and the electrocatalytic performance of the electrocatalyst also have been proven to be significantly improved in oxidizing the methanol in DMFC. Nevertheless, studies on the possible combination of both supported Pt-based alloy electrocatalyst embedding metal oxides as the potential anode nanocomposite electrocatalyst with careful design still lacking and remains important challenge.

The surface properties of YSZ (111) have been investigated by X-ray photoemission spectroscopy (XPS), scanning tunneling microscopy (STM), temperature programmed desorption (TPD) of adsorbed formate, and computational studies using the ReaxFF reactive force field approach. XPS and computer simulations showed enrichment of the surface with yttria. STM studies indicated that a high density of step edges are readily formed with ∼35% of the surface sites located at steps. Step edges are identified as the primary adsorption sites for formate. The formate oxidizes in a dehydration reaction producing carbon monoxide and water at ∼600 K. This is contrasted to the reaction of formate on pure zirconia where formate reacts by both dehydration and dehydrogenation reactions. This shift in the selectivity between pure zirconia and yttria-doped zirconia is attributed to the modification of the active step edge sites by yttria segregation. Therefore, the modification of active sites by minority species in a mixed oxide c...

Chapter 3 - Carbon nitrides as catalyst support in fuel cells: Current scenario and future recommendation

Recent progress in nitrogen-doped carbon and its composites as electrocatalysts for fuel cell applications

In order to reduce the sulfur level in liquid hydrocarbon fuels for environmental protection and fuel cell applications, deep desulfurization of a model diesel fuel and a real diesel fuel was conducted by our SARS (selective adsorption for removing sulfur) process using the adsorbent A-2. Effect of temperature on the desulfurization process was examined. Adsorption desulfurization at ambient temperature, 24 h{sup -1} of LHSV over A-2 is efficient to remove dibenzothiophene (DBT) in the model diesel fuel, but difficult to remove 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT). Adsorption desulfurization at 150 C over A-2 can efficiently remove DBT, 4-MDBT and 4,6-DMDBT in the model diesel fuel. The sulfur content in the model diesel fuel can be reduced to less than 1 ppmw at 150 C without using hydrogen gas. The adsorption capacity corresponding to the break-through point is 6.9 milligram of sulfur per gram of A-2 (mg-S/g-A-2), and the saturate capacity is 13.7 mg-S/g-A-2. Adsorption desulfurization of a commercial diesel fuel with a total sulfur level of 47 ppmw was also performed at ambient temperature and 24 h{sup -1} of LHSV over the adsorbent A-2. The results show that only part of the sulfur compounds existing in the low sulfur diesel can be removed by adsorption over A-2 at such operating conditions, because (1) the all sulfur compounds in the low sulfur diesel are the refractory sulfur compounds that have one or two alkyl groups at the 4- and/or 6-positions of DBT, which inhibit the approach of the sulfur atom to the adsorption site; (2) some compounds coexisting in the commercial low sulfur diesel probably inhibit the interaction between the sulfur compounds and the adsorbent. Further work in determining the optimum operating conditions and screening better adsorbent is desired.

Selective adsorption of tert-butylmercaptan and tetrahydrothiophene on modified activated carbons for fuel processing in fuel cell applications

The co-adsorption of H 2 and CO on Ni(110)

The co-adsorption of H 2 and CO on Ni(110)

Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) using Na-Y and AgNa-Y zeolites for fuel cell applications