Various kinds of amorphous materials, such as transition metal dichalcogenides, metal oxides, and metal phosphates, have demonstrated superior electrocatalytic performance compared with their ...crystalline counterparts. Compared to other materials for electrocatalysis, noble metals exhibit intrinsically high activity and excellent durability. However, it is still very challenging to prepare amorphous noble‐metal nanomaterials due to the strong interatomic metallic bonding. Herein, the discovery of a unique thiol molecule is reported, namely bismuthiol I, which can induce the transformation of Pd nanomaterials from face‐centered‐cubic (fcc) phase into amorphous phase without destroying their integrity. This ligand‐induced amorphization is realized by post‐synthetic ligand exchange under ambient conditions, and is applicable to fcc Pd nanomaterials with different capping ligands. Importantly, the obtained amorphous Pd nanoparticles exhibit remarkably enhanced activity and excellent stability toward electrocatalytic hydrogen evolution in acidic solution. This work provides a facile and effective method for preparing amorphous Pd nanomaterials, and demonstrates their promising electrocatalytic application.
A unique thiol molecule, namely bismuthiol I, is discovered, which can induce the amorphization of Pd nanomaterials by ligand exchange under ambient conditions. This method is applicable to different kinds of Pd nanomaterials without destroying their integrity. Notably, the obtained amorphous Pd nanoparticles show dramatically enhanced electrocatalytic activity and excellent durability toward the hydrogen evolution reaction.
Layered transition metal oxides have drawn much attention as a promising candidate cathode material for sodium‐ion batteries. However, their performance degradation originating from strains and ...lattice phase transitions remains a critical challenge. Herein, a high‐concentration Zn‐substituted NaxMnO2 cathode with strongly suppressed P2–O2 transition is investigated, which exhibits a volume change as low as 1.0% in the charge/discharge process. Such ultralow strain characteristics ensure a stable host for sodium ion storage, which significantly improves the cycling stability and rate capability of the cathode material. Also, the strong coupling between the highly reversible capacity and the doping content of Zn in NaxMnO2 is investigated. It is suggested that a reversible anionic redox reaction can be effectively triggered by Zn ions and is also highly dependent on the Zn content. Such an ion doping strategy could shed light on the design and construction of stable and high‐capacity sodium ion host.
A high‐concentration Zn‐substituted P2‐type is found to exhibit ultralow strain characteristics as a high‐performance sodium‐ion battery cathode. In the sodiation/desodiation process, this P2‐Na2/3Zn0.25Mn0.75O2 exhibits a near zero strain extending along the c‐direction (0.8%) and a small change in volume (1.0%), which significantly improves the cycling stability and rate capability of the cathode material.
A robust porous structure is often needed for practical applications in electrochemical devices, such as fuel cells, batteries, and electrolyzers. While templating approach is useful for the ...preparation of porous materials in general, it is not effective for the synthesis of oxide‐based electrocatalysts owing to the chemical instability of disordered porous materials thus created. Now the synthesis of phase‐pure porous yttrium ruthenate pyrochlore oxide using an unconventional porogen of perchloric acid is presented. The lattice oxygen defects are formed by the mixed‐valence state of Ru4+/5+ through the partial substitution of Ru4+ with Y3+ cations, leading to the formation of mixed B‐site Y2Ru1.6Y0.4O7−δ. This porous Y2Ru1.6Y0.4O7−δ electrocatalyst exhibits a turnover frequency (TOF) of 560 s−1 (at 1.5 V versus RHE) for the oxygen evolution reaction, which is two orders of magnitude higher than that of the RuO2 reference catalyst (5.41 s−1).
Porous Y2Ru1.6Y0.4O7−δ pyrochlore oxide was synthesized using perchloric acid as the unconventional porogen. This pyrochlore exhibited excellent activity towards oxygen evolution reaction (OER) in acid media, with a turnover frequency (TOF) of 560 s−1 (at 1.5 V versus RHE) on the Ru site. A high porous surface area and lattice oxygen defects (due to the partial substitution of B‐site Ru4+ with Y3+) are important for the enhanced OER activity.
The use of 'water-in-salt' electrolytes has considerably expanded the electrochemical window of aqueous lithium-ion batteries to 3 to 4 volts, making it possible to couple high-voltage cathodes with ...low-potential graphite anodes
. However, the limited lithium intercalation capacities (less than 200 milliampere-hours per gram) of typical transition-metal-oxide cathodes
preclude higher energy densities. Partial
or exclusive
anionic redox reactions may achieve higher capacity, but at the expense of reversibility. Here we report a halogen conversion-intercalation chemistry in graphite that produces composite electrodes with a capacity of 243 milliampere-hours per gram (for the total weight of the electrode) at an average potential of 4.2 volts versus Li/Li
. Experimental characterization and modelling attribute this high specific capacity to a densely packed stage-I graphite intercalation compound, C
Br
Cl
, which can form reversibly in water-in-bisalt electrolyte. By coupling this cathode with a passivated graphite anode, we create a 4-volt-class aqueous Li-ion full cell with an energy density of 460 watt-hours per kilogram of total composite electrode and about 100 per cent Coulombic efficiency. This anion conversion-intercalation mechanism combines the high energy densities of the conversion reactions, the excellent reversibility of the intercalation mechanism and the improved safety of aqueous batteries.
Lithium-sulfur batteries are attractive alternatives to lithium-ion batteries because of their high theoretical specific energy and natural abundance of sulfur. However, the practical specific energy ...and cycle life of Li-S pouch cells are significantly limited by the use of thin sulfur electrodes, flooded electrolytes and Li metal degradation. Here we propose a cathode design concept to achieve good Li-S pouch cell performances. The cathode is composed of uniformly embedded ZnS nanoparticles and Co-N-C single-atom catalyst to form double-end binding sites inside a highly oriented macroporous host, which can effectively immobilize and catalytically convert polysulfide intermediates during cycling, thus eliminating the shuttle effect and lithium metal corrosion. The ordered macropores enhance ionic transport under high sulfur loading by forming sufficient triple-phase boundaries between catalyst, conductive support and electrolyte. This design prevents the formation of inactive sulfur (dead sulfur). Our cathode structure shows improved performances in a pouch cell configuration under high sulfur loading and lean electrolyte operation. A 1-A-h-level pouch cell with only 100% lithium excess can deliver a cell specific energy of >300 W h kg
with a Coulombic efficiency >95% for 80 cycles.
The development of cost‐effective catalysts to replace noble metal is attracting increasing interests in many fields of catalysis and energy, and intensive efforts are focused on the integration of ...transition‐metal sites in carbon as noble‐metal‐free candidates. Recently, the discovery of single‐atom dispersed catalyst (SAC) provides a new frontier in heterogeneous catalysis. However, the electrocatalytic application of SAC is still subject to several theoretical and experimental limitations. Further advances depend on a better design of SAC through optimizing its interaction with adsorbates during catalysis. Here, distinctive from previous studies, favorable 3d electronic occupation and enhanced metal–adsorbates interactions in single‐atom centers via the construction of nonplanar coordination is achieved, which is confirmed by advanced X‐ray spectroscopic and electrochemical studies. The as‐designed atomically dispersed cobalt sites within nonplanar coordination show significantly improved catalytic activity and selectivity toward the oxygen reduction reaction, approaching the benchmark Pt‐based catalysts. More importantly, the illustration of the active sites in SAC indicates metal‐natured catalytic sites and a media‐dependent catalytic pathway. Achieving structural and electronic engineering on SAC that promotes its catalytic performances provides a paradigm to bridge the gap between single‐atom catalysts design and electrocatalytic applications.
A paradigm of coordination design and electronic engineering of single‐atom dispersed cobalt catalysts (SAC) is demonstrated, which leads to significantly enhanced electrocatalytic activities and selectivity, therefore presenting new oxygen electrocatalysis pathways via achieving the favored site–adsorbate interactions, and the illustration of the active sites in SAC indicates the metal‐natured catalytic sites and a media‐dependent catalytic pathway.
Batteries with conversion-type electrodes exhibit higher energy storage density but suffer much severer capacity fading than those with the intercalation-type electrodes. The capacity fading has been ...considered as the result of contact failure between the active material and the current collector, or the breakdown of solid electrolyte interphase layer. Here, using a combination of synchrotron X-ray absorption spectroscopy and in situ transmission electron microscopy, we investigate the capacity fading issue of conversion-type materials by studying phase evolution of iron oxide composited structure during later-stage cycles, which is found completely different from its initial lithiation. The accumulative internal passivation phase and the surface layer over cycling enforce a rate-limiting diffusion barrier for the electron transport, which is responsible for the capacity degradation and poor rate capability. This work directly links the performance with the microscopic phase evolution in cycled electrode materials and provides insights into designing conversion-type electrode materials for applications.
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