A considerable amount of platinum (Pt) is required to ensure an adequate rate for the oxygen reduction reaction (ORR) in fuel cells and metal‐air batteries. Thus, the implementation of atomic Pt ...catalysts holds promise for minimizing the Pt content. In this contribution, atomic Pt sites with nitrogen (N) and phosphorus (P) co‐coordination on a carbon matrix (PtNPC) are conceptually predicted and experimentally developed to alter the d‐band center of Pt, thereby promoting the intrinsic ORR activity. PtNPC with a record‐low Pt content (≈0.026 wt %) consequently shows a benchmark‐comparable activity for ORR with an onset of 1.0 VRHE and half‐wave potential of 0.85 VRHE. It also features a high stability in 15 000‐cycle tests and a superior turnover frequency of 6.80 s−1 at 0.9 VRHE. Damjanovic kinetics analysis reveals a tuned ORR kinetics of PtNPC from a mixed 2/4‐electron to a predominately 4‐electron route. It is discovered that coordinated P species significantly shifts d‐band center of Pt atoms, accounting for the exceptional performance of PtNPC.
Phosphorus‐coordinated atomic Pt‐Nx sites are theoretically predicted and experimentally realized, offering enhanced kinetics for four‐electron electrochemical oxygen reduction. Exceptional activity is attributed to the tuning of the d‐band electron center via local coordination asymmetry. This chemistry provides an effective guideline for atomic Pt catalysts in batteries and fuel cells.
Producing indispensable hydrogen and oxygen for social development via water electrolysis shows more prospects than other technologies. Although electrocatalysts have been explored for centuries, a ...universal activity descriptor for both hydrogen‐evolution reaction (HER) and oxygen‐evolution reaction (OER) is not yet developed. Moreover, a unifying concept is not yet established to simultaneously understand HER/OER mechanisms. Here, the relationships between HER/OER activities in three common electrolytes and over ten representative material properties on 12 3d‐metal‐based model oxides are rationally bridged through statistical methodologies. The orbital charge‐transfer energy (Δ) can serve as an ideal universal descriptor, where a neither too large nor too small Δ (≈1 eV) with optimal electron‐cloud density around Fermi level affords the best activities, fulfilling Sabatier's principle. Systematic experiments and computations unravel that pristine oxide with Δ ≈ 1 eV possesses metal‐like high‐valence configurations and active lattice‐oxygen sites to help adsorb key protons in HER and induce lattice‐oxygen participation in the OER, respectively. After reactions, partially generated metals in the HER and high‐valence hydroxides in the OER dominate proton adsorption and couple with pristine lattice‐oxygen activation, respectively. These can be successfully rationalized by the unifying orbital charge‐transfer theory. This work provides the foundation of rational material design and mechanism understanding for many potential applications.
A universal activity descriptor (orbital charge‐transfer energy) is successfully extracted from various materials’ physicochemical properties for both hydrogen‐evolving and oxygen‐evolving reactions in multiple electrolytes. Systematic experiments and computations reveal the life‐cycle HER and OER mechanisms and identify the unifying orbital charge‐transfer theory as a powerful mechanism analysis tool and foundation.
Oxygen‐based anionic redox reactions have recently emerged as a lever to increase the capacity of Mn‐rich layered oxide cathodes in addition to the charge compensation based on cationic redox ...reactions for sodium‐ion batteries. Unfortunately, the irreversibility of anionic redox often aggravates irreversible structure change and poor cycling performance. Here, a stable anionic redox is achieved through substituting Na ions by Mg ions in P2‐type Na0.83Li0.25Mn0.75O2. Density functional theory (DFT) calculations reveal that Mg substitution effectively decreases the oxygen chemical potential, causing an improvement in lattice oxygen stability. Moreover, at a highly desodiated state, Mg ions that remain in the lattice and interact with O 2p orbitals can decrease the undercoordinated oxygen and the nonbonded, electron‐deficient O 2p states, facilitating the reversibility of oxygen redox. When cycled in the voltage range of 2.6–4.5 V where only anionic redox occurs for charge compensation, Na0.773Mg0.03Li0.25Mn0.75O2 presents a much better reversibility, giving a 4 times better cycle stability than that of Na0.83Li0.25Mn0.75O2. Experimentally, Na0.773Mg0.03Li0.25Mn0.75O2 exhibits a ≈1.1% volume expansion during sodium insertion/extraction, suggestive of a “zero‐strain” cathode. Overall, the work opens a new avenue for enhancing anionic reversibility of oxygen‐related Mn‐rich cathodes.
A substitution strategy of partial occupation of the Na‐site by Mg ions in Na0.773Li0.25Mn0.75O2 not only reduces the chemical potential energy of oxygen but also reduces the undercoordinated oxygen, the nonbonded, and electron‐deficient O2p states, thus enhancing the stability of oxygen anodic redox upon long‐term cycling.
Shape control has realized huge success for developing efficient Pd/Pt‐based nanocatalysts, but the control of Ru‐based nanocrystals remains a formidable challenge due to the inherent anisotropy in ...hexagonal closed‐packed nanocrystals. Herein, a class of unique RuCo nanoscrews (NSs) for water electrosplitting is successfully synthesized with rough surfaces and the exposure of steps and edges. Those high‐index faceted RuCo NSs show superior performance for overall water electrosplitting, where a low cell voltage of 1.524 V (@ 10 mA cm−2) and excellent stability for more than 20 h (@ 10 mA cm−2) for overall water electrosplitting in 1 m KOH is achieved. The enhanced performance of RuCo NSs is due to the optimization of the binding energy with the intermediate species and the reduced energy barrier of water dissociation. Density functional theory calculations reveal that the RuCo NS structure intrinsically endows various ridges and edges, which create low coordinated Ru‐ and Co‐sites. These active Ru‐ and Co‐sites present high efficiencies in electronic exchange and transfer between adsorbing O species and nearby lattice sites, guaranteeing the high H2O‐splitting activities. This present work opens up a new strategy for creating high‐performance electrocatalysts for water splitting.
A RuCo electrocatalyst with abundant high index facets is successfully fabricated with superior performance for water‐splitting in an alkaline environment, which is attributed to the simultaneous facilitation of both an alloying effect and high‐index facets. This work supplies significant insights for future research to further overcome the challenge of realizing bimetallic electrocatalysts with high‐index facets.
Redox from the holes at the O2p orbitals is a well‐known phenomenon in Li‐rich Mn‐based batteries. However, such an anionic redox process results in the formation of O2, leading to structural ...instability owing to unstable O2p holes. Herein, a swing‐like non‐isothermal sintering technique is used to stabilize the lattice oxygen by suppressing the formation of O2 during charging. It reduces both the number of intrinsic oxygen vacancies of the Li‐rich Mn‐based oxides and the formation of O2 during charging as compared with traditional constant high‐temperature sintering. Consequently, the number of holes generated during charging in the O2p orbitals increases, whereas the number of unstable O2p holes forming O2 decreases. Therefore, the sample prepared via swing‐like non‐isothermal sintering exhibited considerably slower voltage fading and better cycling stability. This study provides valuable guidelines for stabilizing the lattice oxygen and improving the structural stability of the oxide cathodes for electrochemical energy storage.
This study adopts a swing‐like non‐isothermal sintering technique to stabilize the lattice oxygen of the Li1.2Mn0.54Ni0.13Co0.13O2 cathode. The as‐prepared cathode exhibits high cycling stability. Such enhancement is mainly attributed to the reduced oxygen vacancy concentration during sintering, and facile oxygen reversible oxidation but suppressed O2 release during charging, thereby alleviating the structural transformation.
Li‐rich layered oxides (LRLO) exhibit significant potential for use in all‐solid‐state lithium batteries (ASSLBs) owing to their high capacities and wide range of operating voltages. However, the ...practical application of LRLO in ASSLBs is hindered by the severe failure of carrier transport at the solid–solid interface, which subsequently limits the electrochemical activity of these batteries. Here, the spatially asynchronous activation mechanism of the LRLO in ASSLBs is presented. A spectroscopic study extending from the surface into the bulk interior of LRLO indicates that the activation kinetics of anionic oxygen prefers hysteretic delivery over uniform delivery and fast transition metals (TMs) activation. This spatial hetero activation is dominated by the failure of carrier transport at the interface, which is induced by microstructural defects in the composite cathode. This study is expected to facilitate the microstructural design of high‐performance LRLO‐based ASSLBs.
The carrier transport failure at solid–solid interface induced by the microstructure defects within composite cathode causes the spatial asynchronous activation of Li‐rich cathode in ASSLBs: a sluggish activation of O from the surface to the bulk region throughout the long‐term cycles over a fast and uniform activation of transition metals predominantly occurs in the initial cycle.
Owing to the low theoretical potential of the urea oxidation reaction (UOR), urea electrolysis is an energy‐saving technique for the generation of hydrogen. Herein, a hierarchical structure of CuO ...nanowires decorated with nickel hydroxide supported on 3D Cu foam is constructed. Combined theoretical and experimental analyses demonstrate the high reactivity and selectivity of CuO and Ni(OH)2 toward the UOR instead of the oxygen evolution reaction. The hierarchical structure creates a synergistic effect between the two highly active sites, enabling an exceptional UOR activity with a record low potential of 1.334 V (vs the reversible hydrogen electrode) to reach 100 mA cm−2 and a low Tafel slope of 14 mV dec−1 in 1 m KOH and 0.5 m urea electrolyte. Assembling full urea electrolysis driven by this developed UOR electrocatalyst as the anode and a commercial Pt/C electrocatalyst as the cathode provides a current density of 20 mA cm−2 at a cell voltage of ≈1.36 V with promising operational stability for at least 150 h. This work not only enriches the UOR material family but also significantly advances energy‐saving hydrogen production.
Combined theoretical and experimental analyses demonstrate the high reactivity and selectivity of CuO and Ni(OH)2 toward the urea oxidation reaction (UOR) instead of the oxygen evolution reaction. The hierarchical structure creates a synergistic effect between the two highly active sites, enabling an exceptional UOR activity, which significantly advances energy‐saving hydrogen production.
Abstract
Designing efficient catalyst for the oxygen evolution reaction (OER) is of importance for energy conversion devices. The anionic redox allows formation of O-O bonds and offers higher OER ...activity than the conventional metal sites. Here, we successfully prepare LiNiO
2
with a dominant 3
d
8
L
configuration (
L
is a hole at O 2
p
) under high oxygen pressure, and achieve a double ligand holes 3
d
8
L
2
under OER since one electron removal occurs at O 2
p
orbitals for Ni
III
oxides. LiNiO
2
exhibits super-efficient OER activity among LiMO
2
,
R
MO
3
(M = transition metal,
R
= rare earth) and other unary 3d catalysts. Multiple in situ/operando spectroscopies reveal Ni
III
→Ni
IV
transition together with Li-removal during OER. Our theory indicates that Ni
IV
(3
d
8
L
2
) leads to direct O-O coupling between lattice oxygen and *O intermediates accelerating the OER activity. These findings highlight a new way to design the lattice oxygen redox with enough ligand holes created in OER process.
Spin state transitions and intermetallic charge transfers can essentially change material structural and physical properties while excluding external chemical doping. However, these two effects have ...rarely been found to occur sequentially in a specific material. In this article, we show the realization of these two phenomena in a perovskite oxide PbCoO3 with a simple ABO3 composition under high pressure. PbCoO3 possesses a peculiar A- and B-site ordered charge distribution Pb2+Pb4+ 3Co2+ 2Co3+ 2O12 with insulating behavior at ambient conditions. The high spin Co2+ gradually changes to low spin with increasing pressure up to about 15 GPa, leading to an anomalous increase of resistance magnitude. Between 15 and 30 GPa, the intermetallic charge transfer occurs between Pb4+ and Co2+ cations. The accumulated charge-transfer effect triggers a metal–insulator transition as well as a first-order structural phase transition toward a Tetra.-I phase at the onset of ∼20 GPa near room temperature. On further compression over 30 GPa, the charge transfer completes, giving rise to another first-order structural transformation toward a Tetra.-II phase and the reentrant electrical insulating behavior.
The crystal structure of an orthorhombic YMn0.5Fe0.5O3 (010) (YMFO) epitaxial films on YAlO3(010) substrate was studied using X‐ray diffraction, X‐ray absorption spectroscopy, and anomalous X‐ray ...diffraction techniques. Due to the utmost similar scattering factors of Mn and Fe atoms, it is hard to distinguish them at specific sites of the unit cell from the variations in the diffraction peak intensity. Therefore, anomalous X‐ray scattering was used to determine the order or disorder structure of YMFO films. To estimate the order parameter of the YMFO film, the incident X‐ray energies have been scanned around the Mn K‐edge and Fe K‐edge, resulting in enhanced diffraction intensities of the forbidden YMFO (010) peak by 15–20 times, respectively. This in turn revealed that YMFO films have a partially ordered structure of about 40 ± 10% in the epitaxially grown thin film.
To estimate the amount of order parameter of YMFO films, the incident X‐ray energies have been scanned around the Mn K‐edge and Fe K‐edges, resulting in enhanced diffraction intensities of forbidden YMFO (010) peaks by 15–20 times for Mn and Fe respectively.
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