▶ Recent progress of palladium-based materials including extended surfaces and nanostructured ones for hydrogen oxidation reaction and oxygen reduction reaction was overviewed. ▶ Pd–Pt alloys show ...comparable to or higher hydrogen oxidation activity than pure Pt. ▶ Pd alloys show comparable oxygen reduction activity to pure Pt. ▶ Oxygen reduction activity depends strongly on the orientations of the Pd surface. ▶ Durability of Pd alloys is an issue in fuel cell operation.
Fuel cells, especially low temperature fuel cells are clean energy devices that are expected to help address the energy and environmental problems that have become prevalent in our society. Platinum-based electrocatalysts are usually used as the electrocatalysts for both the anode (hydrogen oxidation) and cathode (oxygen reduction) reactions. The high cost and limited resources of this precious metal hinder the commercialization of fuel cells. Recent efforts have focused on the discovery of palladium-based electrocatalysts with little or no platinum for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR). This paper overviews the recent progress of electrocatalysis of palladium-based materials including both extended surfaces and nanostructured ones for HOR and ORR. The properties of CO and methanol tolerances of palladium-based electrocatalysts are also summarized.
The direct observation of the microstructural evolution and state-of-charge (SOC) distribution in active materials is crucial to understand the lithiation/delithiation mechanisms during ...electrochemical cycling of lithium-ion batteries (LIBs). Owing to their high spatial resolutions and capability to map chemical states by combining other spectroscopic techniques, microscopic techniques including X-ray fluorescence (XRF) microscopy, Raman microscopy, transmission X-ray microscopy (TXM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) play significant roles in real time monitoring the dynamic changes in the LIB electrodes and materials. This paper reviews the recent progress of using in situ microscopic techniques to study LIB materials, including Si-, Sn-, Ge-, C- and metal oxides-based anode materials, and layered oxysulfide, metal fluorides, LiCoO2, LiNi0.8Co0.15Al0.05O2, LiMn2O4, LiFePO4 cathode materials.
•Microstructural evolution and state-of-charge mapping in LIB materials.•Microscopic techniques development and applications in the study of LIBs.•Review and discussion of limitations and advantages of each microscopic technique.
Hydrogen and oxygen evolution reactions (HER and OER) are important for many electrochemical systems. Besides traditional noble-metal-based catalysts, carbon-based materials have been found to be ...effective for catalyzing these reactions. Various carbon structures doped with heteroatoms (N, S, P, B, and transition metals) and graphitic-layer-encapsulated metal and compound particles have shown good activities toward HER and OER at universal pHs. In this Perspective, recent research on the development of carbon-based electrocatalysts for HER and OER, as well as their challenges and opportunities are discussed.
The electrochemical reduction of nitrogen to ammonia on Au-based catalysts showed a reasonably high Coulombic efficiency. The pathway of this promising reaction, however, is not clear partially due ...to the lack of information on reaction intermediates. Herein, surface-enhanced infrared absorption spectroscopy (SEIRAS) was employed to study the reaction mechanisms of nitrogen reduction on an Au thin film for the first time. During the nitrogen reduction, the N2H y species was detected with bands at 1453 (H–N–H bending), 1298 (−NH2 wagging), and 1109 cm–1 (N–N stretching) at potentials below 0 V against reversible hydrogen electrode. This result indicates that the nitrogen reduction reaction on Au surfaces follows an associative mechanism, and the NN bond in N2 tends to break simultaneously with the hydrogen addition. By comparison, no absorption band associated with N was observed on Pt surfaces under the same reaction condition. This result is consistent with the low efficiency of nitrogen reduction on Pt due to the much faster kinetics of hydrogen evolution reaction.
We determined the size-dependent specific and mass activities of the oxygen reduction in HClO4 solutions on the Pt particles in the range of 1–5 nm. The maximal mass activity at 2.2 nm is well ...explained based on density functional theory calculations performed on fully relaxed nanoparticles. The presence of the edge sites is the main reason for the low specific activity in nanoparticles due to very strong oxygen binding energies at these sites. Our results clearly demonstrate that the catalytic activity highly depends on the shape and size of the nanoparticles.
As a promising fuel candidate, ammonia has been successfully used as anode feed in alkaline fuel cells. However, current technology in catalysts for ammonia electro-oxidation reaction (AOR) with ...respect to both cost and performance is inadequate to ensure large scale commercial application of direct ammonia fuel cells. Recent studies found that alloying Pt with different transition metals and controlling the morphology of catalysts can improve the AOR activity, and thus potentially can solve the cost issue. Herein, (100)-terminated Pt-M nanocubes (M = 3d-transition metals Fe, Co, Ni, Zn) are synthesized via wet-chemistry method and their catalytic activities toward AOR are evaluated. The addition of Fe, Co, Ni and Zn elements can enhance the AOR activity due to decrease in oxophilicity of platinum and bifunctional mechanism. Pt-Zn exhibits the maximum mass activity and specific activity with values of 0.41 A/mg
Pt
and 1.69 mA/cm
2
that are 1.6 and 1.8 times higher than Pt nanocubes, respectively. Pt-Fe, Pt-Co and Pt-Ni nanocubes also illustrate higher mass and specific activities compared to Pt nanocubes.
Cu is the only monometallic catalyst that produces a large amount of hydrocarbon fuels during the CO2 electrochemical reduction reaction (CO2RR). However, the CO2RR mechanism and the impact of ...electrolyte are unclear. In this communication, two important issues regarding the CO2RR on Cu surfaces are studied: (1) the direct observation on reaction intermediates and (2) the role of the electrolyte (KHCO3) in the reaction. Surface-enhanced infrared absorption spectroscopy allows direct observation of several reaction intermediates that have never been detected before, except for the commonly detected CO. Another important finding is that CO2 molecules are mediated to the Cu surface via their equilibrium with bicarbonate anions instead of direct adsorption from the solution. These results shed light on the full understanding of the CO2RR on Cu surfaces and developing more advanced catalysts.
We developed a method to engineer well-distributed dicobalt phosphide (Co2P) nanoparticles encapsulated in N,P-doped graphene (Co2P@NPG) as electrocatalysts for hydrogen evolution reaction (HER). We ...fabricated such nanostructure by the absorption of initiator and functional monomers, including acrylamide and phytic acid on graphene oxides, followed by UV-initiated polymerization, then by adsorption of cobalt ions and finally calcination to form N,P-doped graphene structures. Our experimental results show significantly enhanced performance for such engineered nanostructures due to the synergistic effect from nanoparticles encapsulation and nitrogen and phosphorus doping on graphene structures. The obtained Co2P@NPG modified cathode exhibits small overpotentials of only −45 mV at 1 mA cm–2, respectively, with a low Tafel slope of 58 mV dec–1 and high exchange current density of 0.21 mA cm–2 in 0.5 M H2SO4. In addition, encapsulation by N,P-doped graphene effectively prevent nanoparticle from corrosion, exhibiting nearly unfading catalytic performance after 30 h testing. This versatile method also opens a door for unprecedented design and fabrication of novel low-cost metal phosphide electrocatalysts encapsulated by graphene.
The rapid progress of proton exchange membrane fuel cells (PEMFCs) and alkaline exchange membrane fuel cells (AMFCs) has boosted the hydrogen economy concept via diverse energy applications in the ...past decades. For a holistic understanding of the development status of PEMFCs and AMFCs, recent advancements in electrocatalyst design and catalyst layer optimization, along with cell performance in terms of activity and durability in PEMFCs and AMFCs, are summarized here. The activity, stability, and fuel cell performance of different types of electrocatalysts for both oxygen reduction reaction and hydrogen oxidation reaction are discussed and compared. Research directions on the further development of active, stable, and low‐cost electrocatalysts to meet the ultimate commercialization of PEMFCs and AMFCs are also discussed.
The development of fuel cells is of great significance for achieving a sustainable society. Recent progress in cathodic electrocatalysts for proton exchange membrane fuel cells and anodic and cathodic electrocatalysts for alkaline exchange membrane fuel cells is summarized. The rational design strategies, structure evolution, activities, fuel cell performance, and durability of noble‐metal‐ and non‐noble‐metal‐based electrocatalysts are discussed.
The electrochemical surface area (ECA) calculation was studied using the charges associated with stripping of CO and underpotentially deposited H and Cu on highly dispersed Pt- and Pd-based ...nanoparticles. The surface areas followed a general trend of HUPD<CO striping<CuUPD. Transition metals in the alloys were found to have a significant effect on the determination of surface area. The surface area could be underestimated by nearly 50% using HUPD on conventional (non-shape-controlled) PtNi/C. In addition to the effect from Ni, the shape/structure of the nanoparticles also made the calculation more complicated. The surface area could be underestimated by more than two times using HUPD on octahedral PtNi/C compared to using CuUPD. CuUPD was demonstrated to be a more accurate method to estimate the electrochemical active areas than HUPD and CO striping.
•The electrochemical surface areas follow HUPD<CO striping<CuUPD.•Transition metals have a significant effect on area measurement in the Pt alloys.•The area could be underestimated by 2 times using HUPD on octahedral PtNi.•CuUPD is a more accurate method to estimate the electrochemical active areas.
