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.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Localized surface plasmon resonance (LSPR) excitation of noble metal nanoparticles has been shown to accelerate and drive photochemical reactions. Here, LSPR excitation is shown to enhance the ...electrocatalysis of a fuel‐cell‐relevant reaction. The electrocatalyst consists of PdxAg alloy nanotubes (NTs), which combine the catalytic activity of Pd toward the methanol oxidation reaction (MOR) and the visible‐light plasmonic response of Ag. The alloy electrocatalyst exhibits enhanced MOR activity under LSPR excitation with significantly higher current densities and a shift to more positive potentials. The modulation of MOR activity is ascribed primarily to hot holes generated by LSPR excitation of the PdxAg NTs.
Plasmonic excitation of a palladium‐silver alloy nanotube electrocatalyst results in the enhancement of methanol oxidation reaction. Although photothermal heating of the electrochemical interface contributes to the enhancement, the primary mechanism involves hot holes generated by plasmonic excitation. Hot holes drive a methanol oxidation pathway that is complementary to electro‐oxidation.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Fe/N/C is a promising non‐Pt electrocatalyst for the oxygen reduction reaction (ORR), but its catalytic activity is considerably inferior to that of Pt in acidic medium, the environment of polymer ...electrolyte membrane fuel cells (PEMFCs). An improved Fe/N/C catalyst (denoted as Fe/N/C‐SCN) derived from Fe(SCN)3, poly‐m‐phenylenediamine, and carbon black is presented. The advantage of using Fe(SCN)3 as iron source is that the obtained catalyst has a high level of S doping and high surface area, and thus exhibits excellent ORR activity (23 A g−1 at 0.80 V) in 0.1 M H2SO4 solution. When the Fe/N/C‐SCN was applied in a PEMFC as cathode catalyst, the maximal power density could exceed 1 W cm−2.
A non‐precious Fe/N/C electrocatalyst was prepared through pyrolysis of Fe(SCN)3, poly‐m‐phenylenediamine, and carbon black. The obtained Fe/N/C catalyst has high level of S doping and high surface area, and thus exhibits excellent catalytic activity for the oxygen reduction reaction in acidic solution. A polymer electrolyte membrane fuel cell using this catalyst as the cathode can yield a maximal power density as high as 1.03 W cm−2.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Identifying the actual structure and tuning the catalytic activity of Fe–N4‐based moieties, well‐recognized high‐activity sites in the oxygen reduction reaction (ORR) are challenging problems. ...Herein, by using poly(iron phthalocyanine) (PFePc) as an Fe–N4‐based model electrocatalyst, a mechanistic insight into the effect of axial ligands on the ORR catalytic activity of Fe–N4 is provided and it is revealed that the ORR activity of Fe–N4 sites with OH desorption as a rate‐determining step is related to the energy level gap between the OH pxpy and Fe 3dz2, which can be tuned by regulating the field strength of the axial ligands. Thus, PFePc coordinated with a weak‐field ligand I− (PFePc‐I) with a low energy level of Fe 3dz2 exhibits high activity evidenced by an ORR half‐wave potential as high as 0.948 V versus RHE. This work develops a novel strategy for tuning the ORR activity of Fe–N4 and reveals the correlation between the electronic/geometric structure and catalytic activity of Fe–N4.
Structure activity correlation of axial‐coordinated Fe–N4 sites in the oxygen reduction reaction (ORR) is unraveled by studying a series of axial‐coordinated poly(iron phthalocyanine) (PFePc). The energy gap (ηDA) between the Fe 3dz2 and OH px/py is proposed as a new descriptor for the ORR activity of the Fe–N4 sites with OH desorption as a rate‐determining step.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The shapes of noble metal nanocrystals (NCs) are usually defined by polyhedra that are enclosed by {111} and {100} facets, such as cubes, tetrahedra, and octahedra. Platinum NCs of unusual ...tetrahexahedral (THH) shape were prepared at high yield by an electrochemical treatment of Pt nanospheres supported on glassy carbon by a square-wave potential. The single-crystal THH NC is enclosed by 24 high-index facets such as {730}, {210}, and/or {520} surfaces that have a large density of atomic steps and dangling bonds. These high-energy surfaces are stable thermally (to 800°C) and chemically and exhibit much enhanced (up to 400%) catalytic activity for equivalent Pt surface areas for electro-oxidation of small organic fuels such as formic acid and ethanol.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
Nanoparticles of platinum group metals (PGM) supported on diverse substrate materials are widely used catalysts in many important fields such as modern chemical industry, petrochemical industry, ...automobile exhaust purification, and fuel cells. Due to the extremely high cost and rare reserve of the PGM on the earth, to further improve the catalytic activity, stability, and utility efficiency of PGM nanoparticles is the key issue in relevant industrial development as well as the challenge of basic research of science and technology. This feature article summarizes at first the relationship between surface structure and catalytic functionality gained by using metal single-crystal planes as model electrocatalysts, which reveals that high-index planes, i.e., the planes denoted by a set of Miller indices (hkl) with at least one index being larger than unit, with high density of atomic steps and kinks, exhibit generally high catalytic reactivity and stability. Next, guided by the knowledge acquired in model electrocatalysis, we put emphasis upon the electrochemically shape-controlled synthesis of Pt and Pd nanocrystals (NCs) bounded by high-index facets, including tetrahexahedral NCs with 24 {hk0} facets, trapezohedral NCs with 24 {hkk} facets, concave hexoctahedral NCs with 48 {hkl} facets, and multiple twinned nanorods with {hk0} facets. Finally, challenging issues and future prospects in this exciting field are outlined.
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IJS, KILJ, NUK, PNG, UL, UM
Noble metal nanocrystals (NCs) enclosed with high‐index facets hold a high catalytic activity thanks to the high density of low‐coordinated step atoms that they exposed on their surface. ...Shape‐control synthesis of the metal NCs with high‐index facets presents a big challenge owing to the high surface energy of the NCs, and the shape control for metal Rh is even more difficult because of its extraordinarily high surface energy in comparison with Pt, Pd, and Au. The successful synthesis is presented of tetrahexahedral Rh NCs (THH Rh NCs) enclosed by {830} high‐index facets through the dynamic oxygen adsorption/desorption mediated by square‐wave potential. The results demonstrate that the THH Rh NCs exhibit greatly enhanced catalytic activity over commercial Rh black catalyst for the electrooxidation of ethanol and CO.
Tetrahexahedral rhodium nanocrystals (THH Rh NCs) with {830} high‐index facets and high surface energy were prepared for the first time by electrochemical square‐wave‐potential method. The THH Rh NCs exhibit greatly enhanced electrocatalytic activity over commercial Rh black catalyst for the electrooxidation of ethanol (see picture) and CO owing to the high density of step atoms.
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A cathode for high‐rate performance lithium‐ion batteries (LIBs) has been developed from a crystal habit‐tuned nanoplate Li(Li0.17Ni0.25Mn0.58)O2 material, in which the proportion of (010) nanoplates ...(see figure) has been significantly increased. The results demonstrate that the fraction of the surface that is electrochemically active for Li+ transportation is a key criterion for evaluating the different nanostructures of potential LIB materials.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Platinum nanocrystals on carbon black were synthesized by an electrochemical square‐wave potential method (HIF‐Pt/C, see picture). The nanocrystals have high‐index facets and a high density of atomic ...steps. Thanks to this high density, the catalysts exhibit at least twice the activity and selectivity of commercial Pt/C catalysts for ethanol electrooxidation into CO2.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Proton transfer is crucial for electrocatalysis. Accumulating cations at electrochemical interfaces can alter the proton transfer rate and then tune electrocatalytic performance. However, the ...mechanism for regulating proton transfer remains ambiguous. Here, we quantify the cation effect on proton diffusion in solution by hydrogen evolution on microelectrodes, revealing the rate can be suppressed by more than 10 times. Different from the prevalent opinions that proton transport is slowed down by modified electric field, we found water structure imposes a more evident effect on kinetics. FTIR test and path integral molecular dynamics simulation indicate that proton prefers to wander within the hydration shell of cations rather than to hop rapidly along water wires. Low connectivity of water networks disrupted by cations corrupts the fast‐moving path in bulk water. This study highlights the promising way for regulating proton kinetics via a modified water structure.
Accumulating K+ cations break the water network connectivity, and confine protons in the cation hydration shell, thus slowing the proton diffusion kinetics.
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