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Distinctive surface functional groups on 3D MXenes as Pt-supports are correlated with optimized Pt–H affinity and HER activity in alkaline media.

Compared to Ru single atom catalyst, hetero-RuM (M = Fe, Os, and Ir) double atom catalysts showed improved N2RR activity with the help of dxz and dxy bonding orbital, caused by strain, dopant and configurational effects.

With growing interest in the bulk production of the alternative energy carrier hydrogen, dry-reforming of methane using carbon dioxide has attracted great interest as one of the possible carbon capture and utilization (CCU) technologies and hydrogen production methods. An integrated system combining the dry-reforming and water gas shift reactions is suggested to improve the productivity of hydrogen, and a system has also been developed for high-purity hydrogen production from a single system using the sorption-enhanced reaction concept. To realize the proposed system, we develop the Ru-doped Sr0.92Y0.08TiO3 perovskite catalysts and investigate their characteristics using various analyses. The prepared catalysts exhibit excellent CH4 conversion of 92.2% for the dry-reforming reactions at 800 °C without performance degradation by coke formation. Moreover, high-purity hydrogen (>99.5%) is directly produced by the proposed integrated system using anthropogenic greenhouse gases as reactants, and the efficiency is further enhanced by recycling the captured CO2 to the dry-reforming reactor.

As an extension of single-atom catalysts, the development of double-atom catalysts with high electrocatalytic activity for the oxygen evolution reaction (OER) is vital to facilitate hydrogen production and industrial applications. The CoM (M = 3d, 4d, 5d block metals) homo and double-atom catalysts supported on nitrogen-doped graphene (CoM/N

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (Ni3N) nanoparticles were used as earth-abundant metal-based cores to support thin Pt layers. To realize the site-selective formation of Pt layers on the Ni3N core, hydrogen molecules (H2) were used as a mild reducing agent. As H2 oxidation is catalyzed by the surface of Ni3N, the redox reaction between H2 and Pt(IV) in solution was facilitated on the Ni3N surface, which resulted in the selective deposition of Pt on Ni3N. The controlled Pt formation led to a subnanometer (0.5-1 nm)-thick Pt shell on the Ni3N core. By adopting the core-shell structure, higher ORR activity than the commercial Pt/C was achieved. Electrochemical measurements showed that the thin Pt layer on Ni3N nanoparticle exhibits 5 times higher mass activity and specific activity than that of commercial Pt/C. Furthermore, it is expected that the proposed simple wet-chemical method can be utilized to prepare various transition-metal-based core-shell nanocatalysts for a wide range of energy conversion reactions.

PdIr nanoparticles supported on carbon support are synthesized and their oxygen reduction reaction (ORR) activity and durability in a half cell or membrane-electrode assembly (MEA) configuration for polymer electrolyte membrane fuel cell are examined. A synergistic effect of the combination of Pd possessing the effective ORR catalytic activity and Ir as one of the most stable elements in acidic media leads to a decrease in particle size, a higher particle dispersion, and a better ORR activity than Pd monometallic catalysts. It is expected that PdIr alloys would form phase-separated nanoalloys that have Pd-rich surface owing to the higher surface energy of Ir. The addition of Ir to Pd in PdIr/C increases the metallic Pd portion. Meanwhile, the Pd5Ir/C is the most durable compared to Pd/C and Pt/C over 3000 h of MEA operation. The ORR activity of PdIr alloy is expected to increase by reducing the oxygen binding energy of Pd in the presence of Ir from the first-principle calculation, and each contribution of compressive strain and ligand effects is quantified. The cohesive energy and the kinetic segregation energy are also calculated to support the improved stability of PdIr compared to Pd and Pt in the ORR condition.

Herein, binary heteronanosheets made of ultrathin ReS2 nanosheets and reduced graphene oxide (RGO) with either a two-dimensional (2D) “sheet-on-sheet” architecture (2D ReS2/RGO) or a three-dimensio...

Cu-based catalysts have been variously used in the water gas shift reaction (WGSR) and methanol synthesis, both of which use carbon monoxide as a common reactant. According to the Bell–Evans–Polanyi principle, CO adsorption energies (Eads,CO) directly affect the activation energies for CO hydrogenation. Thus, the understanding of the relationship between Eads,CO and the chemical properties of the catalytic surface is fundamental to catalyst design. In particular, recent studies have shown that effective catalysts can be developed by controlling the exposed facets or forming alloys with other transition metal to enhance the mechanical and electronic characteristics. In bimetallic catalysts, two types of chemical effects are known to determine the adsorption energies: one is the “strain” effect caused by lattice mismatch and the other is the “ligand” effect, generated by the change in orbital electrons. We conducted calculations on Cu/M(100), (111), and (211) surfaces (M = Ni, Ir, Pd and Pt) by using spin-polarized density functional theory (DFT) calculations to find the dominant factor, as well as trends, affecting CO adsorption. Our calculations suggest the ligand effect is the dominant contribution to Eads,CO, regardless of the type of facets. We also determined that the ligand contribution is caused by the loss of electrons from the surface Cu atoms. As a result, a proportional correlation between ligand contribution and electron charge transfer was observed. On investigating the strain effect on the (111) facet, we found that the results are consistent with d-band theory, while the Eads,CO on (100) and (211) facets showed the opposite trend.

Herein, we report the synthesis of a strongly coupled Co3O4/CoS microbox heterostructure, prepared through an annealing treatment with the subsequent hydrothermal sulfidation of a Co–Co Prussian blue analog (PBA) precursor. The unique 3D hierarchical architecture and potential synergies of Co3O4 and CoS provide benefits to the Co3O4/CoS heterostructure for both oxygen reduction and evolution reactions (ORR and OER). It displays comparable ORR catalytic activity (half-wave potential of 0.820 V) to state-of-the-art Pt/C but better durability and methanol tolerance. The Co3O4/CoS electrocatalyst also shows high OER activity with a relatively low overpotential (349 mV at 10 mA cm−2) and small Tafel slope (66.6 mV dec−1), compared to those of commercial RuO2 (366 mV at 10 mA cm−2 and 86.3 mV dec−1, respectively), making it a potential bifunctional electrocatalyst for both the ORR and the OER. Moreover, a rechargeable Zn–air battery with a Co3O4/CoS cathode shows a higher cell voltage (1.51 V), higher power density (168 mW cm−2 at 269 mA cm−2), and better cycling stability (up to 150 cycles) than the same battery with the state-of-the-art Pt/C + RuO2 catalyst. This PBA-based material with a strongly coupled interface between Co3O4 and CoS offers insights into the development of low-cost and highly efficient electrocatalysts for diverse energy-related applications.

Efficient hydrogen production is one of the most important issues in the future energy economy. Dehydrogenation of formic acid has been extensively investigated for safe and easy hydrogen production. Thereby, various catalysts have been developed for aqueous formic acid dehydrogenation (FAD) reaction to efficiently produce hydrogen. However, there is still a lack of understanding of the reaction mechanism. Herein, to fundamentally comprehend the aqueous FAD reaction mechanism, we prepared Pd/C catalyst and performed controlled catalytic tests. The results demonstrated that the aqueous FAD reaction occurs through the formate anion dehydrogenation pathway. DFT calculation explained this by the observation that the charge of formate anion significantly mitigates the activation barrier of H-COO bond cleavage. In addition, computational prediction combined with kinetic isotope effect experiments verified that combinative desorption of hydrogen is the rate-determining step of FAD.

CeO2 has been established as an effective scavenger for destructive oxygen radicals in fuel cell membranes. The effect of ceria (CeO2) surface defect on •OH and •OOH radical scavenging efficacy is ...

In this study, aqueous phase reforming (APR) of xylose was conducted over highly dispersed Pt nanoparticles supported on a γ-Al2O3 support (Pt-SNP). Formation of small Pt nanoparticles was confirmed by X-ray diffraction and transmission electron microscopy, which revealed that most of the particles ranged between 0.8 and 1.6 nm in size and the average particle size was 1.3 nm. Temperature-programmed reduction analysis indicated that these small Pt nanoparticles were highly reducible under the reducing environment compared to the commercial Pt/γ-Al2O3 catalysts (Pt-commercial). The catalytic activities of both Pt-SNP and Pt-commercial catalysts were examined in a semi-batch autoclave reactor system for the APR of xylose. It was found that Pt-SNP showed higher carbon to gas conversion with high hydrogen selectivity than Pt-commercial. This was likely due to the increased density of edge sites in the Pt-SNP catalyst that facilitated the cleavage of the C–C bonds rather than the C–O bonds, leading to greater hydrogen production. Furthermore, the Pt-SNP catalyst showed better carbon deposit resistance as compared to Pt-commercial. The amount of carbon deposition on the Pt-SNP catalyst surface and the organic carbon species dissolved in the post-reaction xylose solution were significantly lower compared to that of Pt-commercial. Finally, high purity hydrogen production was achieved using a continuous fixed-bed hybrid reactor including an aqueous phase reformer and a home-made Pd/Ta dense metallic composite membrane. A stable hydrogen gas production (99.999%) was obtained over the Pt-SNP catalyst, which demonstrated the success of a potentially commercial APR reactor system that continuously converted the aqueous xylose solution to hydrogen with high purity.

Polycrystalline alloy electrodes of Pt with alkaline earth metals (Ca, Sr, and Ba) have been shown to exhibit enhanced electrocatalytic performance for oxygen reduction reaction (ORR) relative to P...

In this paper, we report the preparation of highly active and durable ordered intermetallic PdFe catalyst supported on carbon black for formic acid oxidation reaction (FAOR) by high-temperature hea...

Electrochemical hydrogen peroxide (H2O2) production by the direct two-electron (2e-) oxygen reduction reaction (ORR) has received much attention as a promising alternative to the industrially developed anthraquinone fabrication process. Transition metal (M) and nitrogen doped carbon (M-N-C, M = Fe or Co) catalysts are known to be active for four electron ORR pathways via two + two electron transfer, where the former is for the ORR and the latter for the peroxide reduction reaction (PRR). Here, we report mesoporous N-doped carbon/manganese hybrid electrocatalysts composed of MnO and Mn-Nx coupled with N-doped carbons (Mn-O/N@NCs), which have led to the development of electrocatalysis towards the 2e- ORR route. Based on the structural and electrochemical characterization, the number of transferred electrons during the ORR on the Mn-O/N@NCs was found to be close to the theoretical value of the 2e- process, indicating their high activity toward H2O2. The favored ORR process arose due to the increased number of Mn-Nx sites within the mesoporous N-doped carbon materials. Furthermore, there was a strong indication that the PRR is significantly suppressed by adjacent MnO species, demonstrating its highly selective production of H2O2 (>80%) from the oxygen electrochemical process. The results of a real fuel cell device test demonstrated that an Mn-O/N@NC catalyst sustains a very stable current, and we attributed its outstanding activity to a combination of site-dependent facilitation of 2e- transfer and a favorable porosity for mass transport.

Developing highly efficient Ir-based electrocatalysts for the oxygen evolution reaction (OER) has been an important agenda in spearheading the water splitting technology. In this study, the synthesis of IrCo nanocacti on CoxSy nanocages (ICS NCs) is demonstrated by utilizing CoO@CoxSy nanoparticles as reactive nanotemplates. In addition to the high catalytic activities with a low overpotential of 281 mV at 10 mA cm−2 and an outstanding mass activity of 1285 mA mgIr−1 at 1.53 V, the ICS NCs endure a prolonged OER test for over 100 h, greatly outperforming other previously reported Ir-based electrocatalysts. This work suggests that the unique hetero-nanostructure of IrCo/CoxSy induces in situ S doping during electrochemical oxidation and the beneficial effect of S doping on the enhanced stability of ICS NCs for the OER.

There is currently no theoretical study on the hydrogenation of xylose to xylitol on a catalyst's surface, limiting proper understanding of the reaction mechanisms and the design of effective catalysts. In this study, DFT techniques were used for the first time to investigate the mechanisms of xylose to xylitol conversion on five notable transition metal (TM) surfaces: Ru(0001), Pt(111), Pd(111), Rh(111), and Ni(111). Two transition state (TS) paths were investigated: TS Path A and TS Path B. The TS Path B, which was further subdivided into TS Path B1 and B2, was proposed to be the minimum energy path (MEP) for the reaction process. According to our computational results, the MEP for this reaction begins with the structural rearrangement of cyclic xylose into its acyclic form prior to step-wise hydrogenation. The rate-determining step (RDS) on Ru(0001), Pt(111), Pd(111), and Ni(111) was discovered to be the ring-opening process via C-O bond scission of cyclic xylose. On Rh(111), however, the RDS was found to be the first hydrogenation stage, leading to the hydrogenation intermediate. Furthermore, based on the RDS barrier, our results revealed that the activities of the tested TM surfaces follow the trend: Ru(0001) > Rh(111) ≥ Ni(111) > Pd(111) > Pt(111). This result demonstrates the higher activity of Ru(0001) compared to other surfaces used for xylose hydrogenation. It correlates with experimental trends in relation to Ru(0001) superiority and provides the basis for understanding the theoretical design of economical and more active catalysts for xylitol production.

Transition metal phosphides (TMPs) as ever-evolving electrocatalytic materials have attracted increasing attention in water splitting reactions owing to their cost-effective, highly active and stable catalytic properties. This work presents a facile synthetic route to NiCoP nanoparticles with Ru dopants which function as highly efficient electrocatalysts for oxygen evolution reaction (OER) in alkaline media. The Ru dopants induced a high content of Ni and Co vacancies in NiCoP nanoparticles, and the more defective Ru doped NiCoP phase than undoped NiCoP ones led to a greater number of catalytically active sites and improved electrical conductivity after undergoing electrochemical activation. The Ru doped NiCoP catalyst exhibited high OER catalytic performance in alkaline media with a low overpotential of 281 mV at 10 mA cm-2 and a Tafel slope of 42.7 mV dec-1 .

Recently, the polymer electrolyte membrane fuel cell (PEMFC) has been drawing huge attention as an eco-friendly energy conversion device which can replace an internal combustion engine without environmental contaminant such as CO2 and NOx. However, the use of expensive noble metal catalysts such as Pt is essential for the cathode because the oxygen reduction reaction (ORR) at cathode are kinetically much slower than the hydrogen oxidation at anode. For this reason, many of researchers have vigorously worked on the development of Pt-based alloy catalysts such as Pt-Co and Pt-Ni alloys to reduce noble metal usage, but there are still limitations in catalytic activity and durability for the commercialization. Herein, to overcome the limitations, we developed Pt-based carbon-metal hybrid catalyst showing high performance for ORR using density functional theory (DFT) calculation. The slab model of Pt-based carbon-metal hybrid catalyst was constructed by Pt sub-nanocluster supported on graphite with graphene-shaped carbon shell on top of the Pt sub-nanocluster. The most stable geometry of the hybrid catalyst was determined by the formation energy, and the ORR mechanism on surface of hybrid catalyst as well as electrochemical activity was investigated. As a result of investigation, we confirmed that the oxygen reduction occurs on active graphene-shaped carbon shell sites. On pure Pt sub-nanocluster hybrid catalyst, once the hydrogen superoxide (OOH) is adsorbed on carbon shell surface after the oxygen adsorption and protonation, the hydrogen peroxide (H2O2) is preferentially formed at higher onset potential than that of four-electron O2 reduction, which the final product is water (H2O). However, the formation of hydrogen peroxide in PEMFC should be avoided owing to creation of radical, resultant degradation of membrane and low energy conversion efficiency. Surprisingly, we identified that the hydrogen peroxide formed on pure Pt sub-nanocluster hybrid catalyst can be decomposed into OH and H2O with low energy barrier, whose value is much lower than desorption energy of produced hydrogen peroxide, so that subsequent reduction reaction can occur. When this four-electron ORR via hydrogen peroxide decomposition takes place, the ORR activity is improved compared to Pt(111) catalyst, where the onset potential of pure Pt sub-nanocluster hybrid catalyst presents is higher than that of Pt(111). Moreover, we introduced Pt-based alloy sub-nanocluster to reduce Pt usage further. The Pt-based alloy sub-nanocluster hybrid catalyst also exhibited increased ORR activity. For Pt-based alloy sub-nanocluster hybrid catalyst, we carried out analysis of density of state and figured out that the more orbital overlap between carbon shell and sub-nanocluster is generated, the higher catalytic activity is shown due to enrichment of electrons on carbon shell surface. We expect this work can help understanding the mechanism of activity improvement of carbon metal hybrid catalyst, suggesting promising way to design high-performance ORR catalyst with low Pt loadings.

3D customized Pt nanoarchitecture realizes large surface area and porosity for excellent performance and durability in fuel cells., Unsupported Pt electrocatalysts demonstrate excellent electrochemical stability when used in polymer electrolyte membrane fuel cells; however, their extreme thinness and low porosity result in insufficient surface area and high mass transfer resistance. Here, we introduce three-dimensionally (3D) customized, multiscale Pt nanoarchitectures (PtNAs) composed of dense and narrow (for sufficient active sites) and sparse (for improved mass transfer) nanoscale building blocks. The 3D-multiscale PtNA fabricated by ultrahigh-resolution nanotransfer printing exhibited excellent performance (45% enhanced maximum power density) and high durability (only 5% loss of surface area for 5000 cycles) compared to commercial Pt/C. We also theoretically elucidate the relationship between the 3D structures and cell performance using computational fluid dynamics. We expect that the structure-controlled 3D electrocatalysts will introduce a new pathway to design and fabricate high-performance electrocatalysts for fuel cells, as well as various electrochemical devices that require the precision engineering of reaction surfaces and mass transfer.

A simple wet-chemical route for the preparation of core-shell-structured catalysts was developed to achieve high oxygen reduction reaction (ORR) activity with a low Pt loading amount. Nickel nitride (Ni

Molten carbonate fuel cells (MCFCs) are regarded as the closest fuel cell to commercialization due to their high capacity and energy efficiency. However, they are operated at a high temperature (620 °C or higher), where liquid electrolyte loss occurs during operation; hence, their lifetime is limited. For the long-term operation of MCFCs, it is essential to develop a novel method to replenish the electrolyte during operation. However, it is very difficult to directly inject the electrolyte, (Li0.62K0.38)2CO3, into each unit cell of the stack unless it is supplemented through liquid or gas phase at low temperature. It was verified whether LiI and KI, which have low melting points and high vapor pressures, could replenish the lost electrolyte in MCFCs. In this study, the LiI and KI injected into the unit cell in liquid phase showed a similar tendency to the Li/K carbonate electrolyte. This is because LiI and KI react with the CO2/O2 gases supplied to the cathode during MCFC operation to form Li/K carbonate electrolytes.

In this study, Al-foam as a support material is used to reinforce the mechanical strength of the matrix. The use of an Al-foam supported matrix improves mechanical strength but has lower cell performance than using a conventional matrix. The main reasons for the low performance of the cell using the Al-foam supported matrix are short circuit due to leakage current through the Al-foam support and low electrolyte retention capability because of low wettability of aluminum to the liquid electrolytes. To solve these problems, we have developed a process to oxidize the surface of Al-foam reinforced matrix. By observing the unit cell performances, electrochemical analyses and morphological changes according to various oxide thicknesses of the Al-foam support, we have confirmed the optimal oxidation conditions for the Al-foam reinforced matrix. As a result, it was confirmed that the use of an oxidized Al-foam reinforced matrix of about 30 vol% can achieve a cell performance of more than 0.8 V under the current load of 150 mA/cm2 and improve long-term stability.

Catalytic descriptors were studied to design optimum catalysts for the oxidative coupling of methane (OCM) by combining density functional theory (DFT) calculations and actual reaction experiments. SrTiO3 perovskite catalysts, selected for OCM, were modified using metal dopants, and their electronic structures were calculated using the DFT method. The CH3 adsorption energy Eads(CH3) and the oxygen vacancy formation energy Ef(vac) exhibited volcano-type correlations with the C2+ selectivity and O2-consumption for the formation of COx, respectively. The optimum catalytic activity, represented by the C2+ selectivity, was obtained for Eads(CH3) = −2.0 to −1.5 eV, indicating that overly strong adsorption of methyl radicals (or easily dissociated C H bonds of methane) and relatively insufficient oxygen supplementation to the catalyst surface improve deep oxidation to CO and CO2. Praseodymium (Pr)- and neodymium (Nd)-doped SrTiO3 catalysts confirm the DFT-predicted optimum electronic structure of the OCM catalysts.

Proton exchange membrane fuel cells (PEMFCs) are promising mobile power supply systems, and operate without noise or polluting emissions. Because the oxygen reduction reaction (ORR) at the cathode suffers from high overpotential and sluggish kinetics, many catalysts have been developed in efforts to enhance activity and durability for the ORR. However, most of them have complicated synthetic procedures which cannot be scaled-up easily, and have only been tested in a half-cell. High activity in a half-cell does not necessarily guarantee better performance in a single-cell. In this work, we synthesized an Au-doped PtCo/C catalyst using a simple method of gas-phase reduction and subsequent galvanic replacement, and its activity and durability were tested in a single-cell. When current densities were compared at 0.6 V after a durability test of 30,000 cycles in 0.6–1.0 V, the values were 1.40, 0.81, and 0.63 A cm−2 for the Au-doped PtCo/C, acid-treated PtCo/C, and commercial Pt/C catalysts, respectively. Co leaching was much less in the Au-doped PtCo/C. Density functional theory (DFT) calculations confirmed that surface oxygen species bound more weakly at the catalyst surface and migration of a Co atom (Co segregation) to the surface was suppressed in the presence of Au. This facile method can provide a more realistic strategy to design better ORR catalysts for PEMFC application.

To improve the microstructural and electrochemical properties of gadolinium-doped ceria (GDC) electrolytes, materials co-doped with 0.5–2 mol% of lithium and cobalt oxides were successfully prepared in a one-step sol gel combustion synthesis route. Vegard's slope theory was used to predict the dopant solubility and the sintering behaviour. The charge and size of the added dopant influence the atom flux near the grain boundary with a change in the lattice parameter. In fact, compared to traditional multi grinding steps, sol gel combustion facilitates molecular mixing of the precursors and substitution of the dopant cations into the fluorite structure, considerably reducing the sintering temperature. Adding precursors of lithium and cobalt, as dopant, increases the GDC densification and reduces its traditional sintering temperature down to 1000–1100 °C, with an improvement of electrochemical properties. Impedance analysis showed that the addition of 2 mol% of lithium or 0.5 mol% of cobalt enhances the conductivity with a consequent improvement of cell performances. High total conductivities of 1.26·10−1 S cm−1 and 8.72·10−2 S cm−1 at 800 °C were achieved after sintering at 1000 °C and 1100 °C for 2LiGDC and 0.5CoGDC, respectively.

In this work, we unravel the beneficial role of the Zn ensemble (in particular, an a single Zn atom) in the sixfold-coordinated kinked (Cu-vacant) site of the stepped Cu(2 1 1) surface for enhancing the reactivity and durability of catalyst in the CH3OH production from CO2 and H2. For such purpose, by using the density functional theory (DFT) and microkinetic modeling methods, we systematically calculate the catalytic properties (activation energy barrier, turn of frequency (TOF), and rate constant), physical properties (cohesive and formation energy) and electronic structures (local density of state, and local charge distribution) of the different defective Cu sites [such as the stepped, kinked, Zn-substituted stepped Cu(2 1 1) surfaces] and the different Zn ensembles [dimer, and linear ensemble]. First, our DFT calculations exhibit that the Zn atoms at the sevenfold-coordinated site of the Cu(2 1 1) surface tend to be isolated and acts as the modifier to suppress the loss of Cu atoms from the stepped Cu(2 1 1) surface. Second, we find that the catalysis of CH3OH synthesis strongly depends on the type of defects at the Cu(2 1 1) surface. In particular, the single Zn atom-substituted (sevenfold-coordinated) stepped site in the Cu(2 1 1) surface is found to have the superior catalytic activity (TOF = 3.07 × 10−5 s−1 @ P = 75 bar and T = 523 K) toward the CH3OH formation compared to the traditionally-known active Cu(2 1 1) surface (TOF = 2.73 × 10−7 s−1). In contrast, the sixfold-coordinated kinked site is determined to largely slow down the rate of CH3OH production (TOF = 3.34 × 10−15 s−1). The increased catalysis in the Zn-associated stepped site is related to the significant enhancement of the surface affinity toward the adsorbate having the oxygen moiety (especially, HCOO), which leads to the large reduction of the activation energy barrier in the initial energy-demanding CO2 hydrogenation reaction and in turn the improved catalysis of CH3OH synthesis. Our DFT calculation also elucidates that the stronger covalent-like overlap between O 2p—Zn 3d electrons (which is caused by the electronic charge loss of the Zn atom to the near-neighboring Cu sites) than the O 2p—Cu 3d case is responsible for such enhanced affinity of oxygen-containing adsorbates. In addition, we found that the single Zn atom exhibit the highest activity of CH3OH production (TOFCH3OH = 3.07 × 10−5 s−1) over the dimer (1.62 × 10−7 s−11) and linear ensemble (5.53 × 10−7 s−1), which is related to the weaker affinity of Zn with H than the Cu-H case, which leads to the low coverage of surface H atom and in turn retard the CH3OH production via CH3O hydrogenation. Our study highlights the novel strategy of engineering the activity and stability of the defective undercoordinated kinked site for the enhanced CH3OH synthesis from CO2 and H2 by controlling the arrangement of surface Zn atom at the stepped Cu(2 1 1) surface.

Lithium-gadolinium-doped ceria electrolytes (2–5 mol% of lithium) are prepared by fast and reliable one-pot sol gel combustion synthesis and sintered at low temperature. The aim is to improve the microstructure, electrochemical and power generation of electrolyte-supported intermediate temperature solid oxide fuel cells. Time-of-flight coupled secondary ions mass spectroscopy and transmission electron microscopy reveal the uniform distribution of lithium and the structural modification and surface change induced by the doping. Lithium addition reduces the sintering temperature to 950 °C, and the electrochemical properties compared to the pure gadolinium doped ceria are highly superior. A maximum of 3.59·10−2–1.41·10−1 S·cm−1 for total conductivity are achieved for 3 mol.% of lithium addition at intermediate operative temperature range. An electrolyte-supported solid oxide fuel cell is then fabricated and tested in different gas conditions and operative temperatures. The maximum power density is 359 mW·cm−2 at 668 mA·cm−2 (750 °C). The results demonstrate the reliability, the short time-to-product and the feasibility of both synthesis cycle and electrolyte production for industrial application to develop a cost-effective and marketable fuel cell technology.

The catalytic partial oxidation of methane is evaluated over a Rh (2–15 mol%)-doped Sr0.92Y0.08TiO3-δ (SYT) perovskite-based catalyst prepared by the Pechini method for fuel-cell applications. The Rh dopant replaces titanium in the SYT catalyst, resulting in a catalyst with excellent and stable catalytic performance during thermal cycling in the temperature range 600–900 °C and in long-term stability tests at 750 °C for 130 h, without deactivation due to carbon coking or sintering. A systematic round-robin characterization is carried out by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and CO chemisorption to establish the chemical and physical properties of the catalyst. Adding Rh as a dopant in the catalyst significantly promotes the catalytic activity due to the presence of exsoluted rhodium particles on the catalyst surface. Small particles (2–5 nm) of Rh on the SYT surface are observed to be evenly dispersed, without agglomeration, and the turnover frequency (TOF) of the POM reaction increased. In the long-term stability tests, catalysts are tested in direct internal reforming at an SOFC anode, achieving high methane conversion (∼99%) in both dry and wet conditions.

Biofuels such as sewage gas and landfill gas, which can be used as fuels in solid oxide fuel cells, have suitable composition of CH4 and CO2 for dry reforming. We developed an Sr0.92Y0.08Ti1−xRuxO3−d material as an anode for solid oxide fuel cells that use biofuels as a direct fuel and show an excellent performance in dry reforming. The Pechini method was used to synthesize the material using ruthenium substitution in the titanium site of an Sr0.92Y0.08TiO3−d (SYT) material. X-ray diffraction analysis confirmed that the perovskite phase of the synthesized catalyst was maintained. Ruthenium-loaded catalysts were prepared by coprecipitating ruthenium onto SYT to compare with the Sr0.92Y0.08Ti1−xRuxO3−d. The differences between Sr0.92Y0.08Ti1−xRuxO3−d and ruthenium-loaded SYT materials during methane dry reforming and the thermal stability during long-term operation were evaluated. In particular, SYTRu10 exhibited higher methane conversion and carbon dioxide conversion than Ru10-loaded SYT at the temperature range of 600–900 °C and stable performance even in long-term operation. X-ray fluorescence and Brunauer–Emmett–Teller measurements were performed to measure the composition of the catalysts and the specific surface area, pore size, and pore volume of the catalysts. X-ray photoelectron spectroscopy and temperature-programmed reduction were used to investigate the state and behavior of ruthenium. Furthermore, transmission electron microscopy was performed to analyze the shape of the catalyst before and after the reaction.

Carbon blacks, which consist of the assemblies of small graphene clusters having a spherical concentric packing structure, are amorphous and have widely been used as catalyst supports for proton exchange membrane fuel cell (PEMFC) electrodes. However, poor electrochemical corrosion resistance during extended use and repeated cyclic operation of PEMFCs shortens their practical device lifetime; surface defects, such as nanosized disordered domains, have been established as the most influential factors. Herein, we coupled polymeric graphitic carbon nitride (pg-CN) with amorphous carbon black (a-CB) in a core@shell structure to produce an electrochemically efficient and stable electrocatalyst support. Our protocol allowed for the simultaneous optimization of uniformly thin graphitic shell structures for electrochemical corrosion stability and nitrogen-enriched functionalities on the carbon surfaces for electrocatalyst (e.g., platinum) nucleation. The newly prepared a-CB@pg-CNs enhanced the stable fuel cell devices operation and remained invariant even at high potential (1.2–1.7 V). Significantly, when used for constructing the PEMFC electrode, a-CB@pg-CN support-based Pt catalyst electrodes outperformed and exhibited superior stability over state-of-the-art commercial a-CB-based counterparts. Experimental observations and density functional theory (DFT) calculations revealed that the unusual electrocatalytic properties of as-prepared a-CB@pg-CNs originated from an intrinsic chemical and electronic coupling that synergistically reduced electrochemical corrosion kinetics and promoted catalyst–support interactions.

Despite recent efforts on replacing a noble Pt to less expensive catalysts (such as Pt-Ni and Pt-Co alloys) for improving oxygen reduction reaction (ORR) for PEMFC (polymer electrolyte membrane fuel cell) application, the performance and stability of a noble Pt catalyst still remains superior. In the present study, we have proposed the systematic procedure for designing the Ir3M (M = 3d, 4 d, 5 d transition metal) nanoalloy as Pt alternatives with enhanced ORR activity and stability using density functional theory (DFT) and experimental methods. First, we computationally optimized the surface occupied/unoccupied d states and lattice distance of the thermodynamically-stable Ir3M nanoalloy in order to achieve the wanted oxygen affinity for promoting ORR. In the next screening process, the nanoalloy prone to the segregation of inside M atom toward the surface layer was excluded, leading ultimately to the potential candidates such as the pure Ir monolayer on the top of Ir3Cr, Ir3V, Ir3Re, and Ir3Tc alloy cores. Finally, a pure Ir monolayer on the top of Ir3Cr core (which was expected to show the most enhanced ORR activity among the computationally-screened candidates) was experimentally prepared via physical vapor deposition method (PVD) and electrochemically evaluated for confirming our DFT prediction. Our synthesis successfully produced a 3 nm Ir-covered (so-called Ir skinlayer) Ir3Cr nanoparticle (Ir/Ir3Cr), which displayed the surface lattice contraction by 1.03% compared to the pure Ir case. The specific activity (at 0.7 V vs RHE) of a Ir/Ir3Cr catalyst with the very high durability (showing only 0.05% decrease from the initial activity after 3000 potential cycles) was 12.3 times higher than a Ir catalyst. The detail mechanism on the enhanced activity in Ir-M alloy was also examined. The design principle of alloy catalysts used in this study can be further extended to the screening of catalytic materials for the application to the next-level electrochemical reaction.

Herein, binary heteronanosheets made of ultrathin ReS