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In this work, we show an effective strategy combining experimental and computational methods to explore and clarify rational design approaches utilizing transition metals for enhanced electrocatalysis of oxygen reactions. We report a bifunctional electrocatalyst synthesized by a chemical deposition of palladium (Pd) nanoparticles on three-dimensionally ordered mesoporous cobalt oxide (Pd@3DOM-Co3O4) demonstrating extreme stability and activity towards electrocatalytic oxygen reduction and evolution reactions (ORR and OER). Pd@3DOM-Co3O4 exhibits a significantly positive-shifted ORR half-wave potential of 0.88 V (vs. RHE) and a higher OER current density of 41.3 mA cm−2 measured at 2.0 V (vs. RHE) relative to non-deposited 3DOM-Co3O4. Moreover, in terms of durability, Pd@3DOM-Co3O4 demonstrates a negligible half-wave potential loss with 99.5% retention during ORR and a high current density retention of 96.4% during OER after 1000 cycles of accelerated degradation testing (ADT). Ab-initio computational simulation of the oxygen reactions reveals that the modification of the electronic structure by combining Pd and Co3O4 lowers the Pd d-band center and enhances the electron abundance at the Fermi level, resulting in improved kinetics and conductivity. Furthermore, it is elucidated that the enhanced electrochemical stability is attributed to an elevated carbon corrosion potential (Ucorr,C) for the Pd@3DOM-Co3O4 surface and an increased dissolution potential (Udiss) of Pd nanoparticles. Meanwhile, synergistic improvements in the bifunctional activity resulting from the combination of Pd and 3DOM-Co3O4 were confirmed by both electrochemical and physical characterization methods, which highlights the practical viability of Pd@3DOM-Co3O4 as an efficient bifunctional catalyst for rechargeable metal-air batteries.

Developing high-efficiency and cost-efficient electrodes for hydrogen and oxygen evolution reactions (HER and OER respectively) is a major challenge in water electrolysis technology. We developed a chemical transformation route that can produce both high-performance OER and HER electrodes by corrosion of a Ni foam and subsequent phosphidation process, which generated ternary NiFeCo layered double hydroxide (LDH) and phosphide nanosheets supported on the foam, respectively. Because of their compositions and high electrical conductivities, these ternary LDH and phosphide electrodes exhibited remarkably high activities for OER and HER, respectively, outperforming most of other catalysts reported to date. An alkaline water electrolyzer based on these electrodes achieved a current density of 10 mA/cm2 at an only 1.47 Vcell. In addition, anion exchange membrane water electrolyzer based on these electrodes reached a current density of 500 mA/cm2 at an only 1.75 Vcell.

Ni-based electrocatalysts for replacement of precious metal electrocatalyst, the cathode materials of anion exchange membrane water electrolyzer (AEMWE), are seriously unstable and low activity at hydrogen production conditions. This study develops a high-performance, durable non-precious metal electrocatalyst for AEMWE, which show improved activity and durability. First, Ni/C was alloyed with Co and supported on carbon cloth coated with microporous carbon layer to improve the electrocatalytic activity of the hydrogen evolution reaction (HER) electrocatalyst; then, oxide (Ni/Co-O) was locally formed on the synthesized NiCo/C to increase its activity and durability. Specifically, this oxide increased the coverage of OH− ions, formed hydrogen spillover channels, and promoted the HER. Further, its improved electrochemical durability was attributed to the high bond dissociation energy of the metal oxide. The electrocatalyst was also evaluated as the cathode in single-cell (1-cell) and stack cell (5-cell) AEMWE systems to demonstrate that this superior performance would translate to the commercial scale.

A chemically etched CuCo-oxide (CE-CCO) electrode prepared by electrodeposition was used for oxygen evolution reaction electrocatalyst. Surface chemical etching of CuCo-oxide (CCO) introduced oxygen vacancies and thus increased electrical conductivity to promote oxygen generation. During practical applicability testing, when CE-CCO was used as the anode of an anion-exchange membrane water electrolyzer, enhanced oxygen evolution performance was observed (current density = 1390 mA/cm2 at 1.8 Vcell), which, among other reactions, was ascribed to the easy removal of O2 from the aerophobic electrode surface. In addition to featuring low mass transfer resistance even at high current density with substantial gas generation, the CE-CCO electrode featured remarkable durability, exhibiting stable performance over 3600 h under the conditions of continuous O2 evolution. Thus, this work shows that the performance of electrodeposited oxide catalysts can be enhanced by introducing oxygen vacancies, while the energy conversion efficiency of the corresponding water electrolysis systems can be increased by lowering mass transfer resistance via efficient gas removal and reactant supply.

a b s t r a c t Oxygen reduction and ethanol oxidation reaction (ORR and EOR) have been studied on graphene nanosheet-supported (GNS) pure Pd and Pd3Y nanoscale-alloy (Pd/GNS and Pd3Y/GNS) electrocatalysts. The electrochemical studies were carried out for ORR both in acidic and alkaline solutions employing a rotating disk electrode (RDE), and performed for EOR in alkaline media with cyclic voltammetry method. The structure and composition of the Pd and Pd3Y nanoparticles were verified using TEM, XRD and XPS. We combine the experimental measurements with ab initio density functional theory (DFT) calculations to identify the d-band center position of Pd atom in the pure Pd and Pd3Y alloys as a function of site on near the surface. Both approaches clearly show that alloying the Pd with Y significantly modifies the electronic structures of Pd atoms. Core-level of Pd 3d5/2 shifts to a negative value, which increases the d-band center of Pd atom and enhances the bond strength of Pd O, which implies good catalysts for EOR but ORR. Our results indicate that the electronic structure of the Y-modified bimetallic Pd alloy is a good descriptor for the catalytic activity.

Electrocatalytic oxidations of ethylene glycol and glycerol were studied over a carbon-supported PtRuSn catalyst (PtRuSn/C), which was prepared with a Pt:Ru:Sn atomic ratio of 5:4:1 using a colloidal method combined with a freeze-drying procedure at room temperature. The ternary PtRuSn/C catalyst was characterized by various physicochemical analyses such as X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and X-ray absorption-near-edge spectroscopy (XANES). The ternary PtRuSn catalyst showed noticeable modifications on the catalyst phases from Pt or PtRu in regards to structural and electronic features, such as a change in lattice parameter and electronic modification in unfilled d band states of Pt atoms. The structurally and electronically modified PtRuSn/C catalysts substantially enhanced the electrocatalytic activities for ethylene glycol and glycerol oxidations, resulting in larger peak currents and lower onset potentials of the electrooxidations. By incorporating the Ru and Sn elements onto the ternary PtRuSn/C catalyst, efficient oxidative removals of CO or CO-like carbonaceous intermediate species produced during the reaction were also possible, thus preventing poisoning of the active Pt sites. Consequently, significant enhancements of electrocatalytic activity and stability over the ternary PtRuSn/C catalyst could be achieved for the electrooxidations of ethylene glycol and glycerol.

A series of carbon-supported bimetallic PtSn catalysts for the electrooxidation of C1–C3 alcohols (i.e., methanol (C1), ethanol (C2), and 1-propanol (C3)) were prepared with different Pt:Sn atomic ratios using borohydride reduction method combined with freeze-drying procedure at room temperature. The catalysts were investigated by employing various physicochemical analyses: X-ray diffraction (XRD), transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) to investigate the structural modification, and X-ray photoelectron spectroscopy (XPS) and X-ray absorption-near-edge spectroscopy (XANES) to characterize the change in electronic features. The variation of Sn content by forming PtSn alloys causes significant structural and electronic modifications of Pt crystallites, resulting in increases of lattice parameter and decreases of the Pt 5d band vacancies with Sn content. Cyclic voltammetry (CV) measurements showed that the addition of Sn into the Pt catalyst promotes the electro-catalytic activities for the electrooxidations of C1, C2, and C3 alcohols, in which the maximum activities appeared at different Sn contents for the C1–C3 alcohols. In particular, a shift in optimum Pt:Sn composition was observed in that the Sn content required to reach the maximum peak current density was increased with the increasing number of carbon atoms in the C1–C3 alcohols. Both the geometric and electronic effects with variation of Sn content are in close relationship in the bimetallic PtSn catalysts, consequently affecting the electrocatalytic activities by showing volcano-type behaviors over the electrooxidation of the individual alcohol.