The low hydrogen adsorption free energy and strong acid/alkaline resistance of layered MoS2 render it an excellent pH‐universal electrocatalyst for hydrogen evolution reaction (HER). However, the ...catalytic activity is dominantly suppressed by its limited active‐edge‐site density. Herein, a new strategy is reported for making a class of strongly coupled MoS2 nanosheet–carbon macroporous hybrid catalysts with engineered unsaturated sulfur edges for boosting HER catalysis by controlling the precursor decomposition and subsequent sodiation/desodiation. Both surface chemical state analysis and first‐principles calculations verify that the resultant catalysts exhibit a desirable valence‐electron state with high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, significantly improving the intrinsic HER catalytic activity. Such an electrocatalyst exhibits superior and stable catalytic activity toward HER with small overpotentials of 136 mV in 0.5 m H2SO4 and 155 mV in 1 m KOH at 10 mA cm−2, which is the best report for MoS2–C hybrid electrocatalysts to date. This work paves a new avenue to improve the intrinsic catalytic activity of 2D materials for hydrogen generation.
A class of strongly coupled MoS2 nanosheet–carbon macroporous hybrids with engineered unsaturated sulfur edges has been developed as excellent hydrogen evolution reaction (HER) electrocatalysts. Both experimental analysis and first‐principles calculations verify that the resultant catalysts exhibit high exposure of unsaturated sulfur edges and an optimized hydrogen adsorption free energy, greatly boosting the HER activity and durability in acidic and alkaline media.
Abstract
Water dissociation (WD, H
2
O → H
+
+ OH
−
) is the core process in bipolar membranes (BPMs) that limits energy efficiency. Both electric-field and catalytic effects have been invoked to ...describe WD, but the interplay of the two and the underlying design principles for WD catalysts remain unclear. Using precise layers of metal-oxide nanoparticles, membrane-electrolyzer platforms, materials characterization, and impedance analysis, we illustrate the role of electronic conductivity in modulating the performance of WD catalysts in the BPM junction through screening and focusing the interfacial electric field and thus electrochemical potential gradients. In contrast, the ionic conductivity of the same layer is not a significant factor in limiting performance. BPM water electrolyzers, optimized via these findings, use ~30-nm-diameter anatase TiO
2
as an earth-abundant WD catalyst, and generate O
2
and H
2
at 500 mA cm
−2
with a record-low total cell voltage below 2 V. These advanced BPMs might accelerate deployment of new electrodialysis, carbon-capture, and carbon-utilization technology.
•Emerging anion-exchange membrane water electrolysis (AEMWE) is introduced.•Transition metal-based powder and self-supporting catalysts for AEMWE are summed.•A detailed guideline for establishing the ...AEMWE testing system is provided.•Advanced electrochemical methods to evaluate the AEMWE performance are elaborated.
Green hydrogen produced by water electrolysis is one of the most promising technologies to realize the efficient utilization of intermittent renewable energy and the decarbonizing future. Among various electrolysis technologies, the emerging anion-exchange membrane water electrolysis (AEMWE) shows the most potential for producing green hydrogen at a competitive price. In this review, we demonstrate a comprehensive introduction to AEMWE including the advanced electrode design, the lab-scaled testing system establishment, and the electrochemical performance evaluation. Specifically, recent progress in developing high activity transition metal-based powder electrocatalysts and self-supporting electrodes for AEMWE is summarized. To improve the synergistic transfer behaviors between electron, charge, water, and gas inside the gas diffusion electrode (GDE), two optimizing strategies are concluded by regulating the pore structure and interfacial chemistry. Moreover, we provide a detailed guideline for establishing the AEMWE testing system and selecting the electrolyzer components. The influences of the membrane electrode assembly (MEA) technologies and operation conditions on cell performance are also discussed. Besides, diverse electrochemical methods to evaluate the activity and stability, implement the failure analyses, and realize the in-situ characterizations are elaborated. In end, some perspectives about the optimization of interfacial environment and cost assessments have been proposed for the development of advanced and durable AEMWE.
Display omitted
Abstract
In alkaline and neutral MEA CO
2
electrolyzers, CO
2
rapidly converts to (bi)carbonate, imposing a significant energy penalty arising from separating CO
2
from the anode gas outlets. Here we ...report a CO
2
electrolyzer uses a bipolar membrane (BPM) to convert (bi)carbonate back to CO
2
, preventing crossover; and that surpasses the single-pass utilization (SPU) limit (25% for multi-carbon products, C
2+
) suffered by previous neutral-media electrolyzers. We employ a stationary unbuffered catholyte layer between BPM and cathode to promote C
2+
products while ensuring that (bi)carbonate is converted back, in situ, to CO
2
near the cathode. We develop a model that enables the design of the catholyte layer, finding that limiting the diffusion path length of reverted CO
2
to ~10 μm balances the CO
2
diffusion flux with the regeneration rate. We report a single-pass CO
2
utilization of 78%, which lowers the energy associated with downstream separation of CO
2
by 10× compared with past systems.
Display omitted
•Rapid low-temperature synthesis of hollow CuS0.55 nanoparticles has been shown.•The hollow nanostructure greatly improves electrochemically active surface area.•The rich Cu sites ...show strong adsorption ability to targeted OOH∗ intermediates.•An ultralow overpotential is required for water oxidation in alkaline media.
Developing low-cost and binder-free Cu-based electrocatalysts for high-performance oxygen evolution reactions (OER) is of great importance to promote their practical applications. Herein, we demonstrate the low-temperature and rapid synthesis of hollow CuS0.55 nanoparticles on a Cu foam as highly active OER electrocatalysts through an anodic oxidation electrodeposition technique. The large electrochemically active surface area and strong adsorption ability of Cu sites to targeted OOH∗ intermediates are beneficial for enhancing catalytic properties. As a consequence, the hollow CuS0.55 nanoparticles exhibit an ultralow overpotential of 386 mV to achieve a high current density of 100 mA cm−2 in alkaline media with a very small Tafel slope of 33 mV dec−1, which is among the best reported for Cu-based electrocatalysts. The turnover frequency (TOF) is approximately 6 times higher than those of the corresponding CuS0.57 and CuO catalysts. This work provides a simple and feasible approach that can be scaled up easily to construct low-cost and efficient Cu-based OER electrocatalysts.
Breaking the scaling relationship of water oxidation is the gateway to obtain an ultrahigh current density at a low potential for greatly improving the water electrolysis efficiency in industrial ...hydrogen production. Herein, we demonstrate a novel heterointerface engineered NiFe(OH)
x
/Ni
3
S
2
electrocatalyst to successfully circumvent the scaling relationship of the oxygen evolution reaction (OER), which significantly decreases the difference of the Gibbs free energy of HOO* and HO*(}ΔG
hoo*
–ΔG
ho*
) from 3.20 to 2.38 eV. To achieve an ultrahigh current density of 2000 mA cm
−2
, the NiFe(OH)
x
/Ni
3
S
2
electrocatalyst requires a small overpotential of 310 mV with an ultralow Tafel slope of 20.8 mV dec
−1
. It can also steadily operate under 1000 mA cm
−2
for over 100 h with insignificant activity loss, thus surpassing the state-of-the-art OER catalysts to date. A parallel catalytic mechanism has been disclosed to be responsible for the optimization of the reaction pathway, thus realizing the homogenization of multi-intermediate adsorption energy with extremely elevated OER catalytic performance at ultrahigh current densities. These findings could be a guidance in developing industrial-grade high-performance electrocatalysts for water splitting.
Exploring cost-effective and highly-active oxygen evolution reaction (OER) electrocatalysts is a pressing task to propel water electrolysis for green hydrogen production. Herein, we constructed a ...class of Fe-doped and S-enriched Ni3S2 nanowires electrocatalysts for optimizing the target intermediates adsorption to decrease the OER overpotentials at various current densities. The optimal Ni3S2-1.4%Fe electrocatalyst possesses the most active sites and exhibits an ultralow overpotential of 190 mV at 10 mA cm−2 with an excellent stability of > 60 h, exceeding the majority of recently-reported Ni3S2-based electrocatalysts. The trivalence Fe-doping not only reduces the electron density of the Ni center, but also enables the sulfur enrichment on the Ni3S2 surface, which greatly improves the intrinsic activity and the number of target intermediates (∗OOH). A novel methanol-assisted electrochemical evaluation further reveals that the Ni3S2-1.4%Fe electrocatalyst demonstrates a weaker binding ability to ∗OH with the rapid generation of ∗OOH species, and thus gives a lower apparent activation energy compared with the surface sulfur reduced ones. This work provides a new perspective for regulating the adsorption of intermediates through doping strategy.
Display omitted
•Fe-doped and sulfur-enriched Ni3S2 nanowires electrocatalysts are demonstrated.•The trivalence Fe-doping improves the intrinsic activity and target intermediates.•The Ni3S2-1.4%Fe electrocatalyst shows a low overpotential for oxygen evolution.
With the steady increase of air traffic column, an auxiliary decision tool is required to compensate the operation redundancy deficiency of more sectors of air traffic control. To solve the problem ...of nonconflict high-density departure and arrival traffic flow, this method is expected to rapidly establish and maintain safe separation with more flexible changing strategies for aircraft heading and speed. This paper proposes an improved reinforcement learning framework to achieve conflict detection and resolution. The proposed framework includes the first development of an air traffic flow model based on a multiagent Markov decision process. The goal reward function was then maximized by improved Monte-Carlo tree search combined with an upper confidence bound tree. Three simulation scenarios were designed for illustrating the improvements of the proposed algorithm, with the results indicating that the algorithm could establish and maintain safe separation between 20 agents in the simplified hexagon-shaped airspace of Huadong, China. Furthermore, the proposed method was demonstrated to reduce the number of conflicts between aircraft agents by up to 26.32% compared to previous research.
Air transportation is a huge, complex system with emergence and self-organization, which makes it important for it to be modelled. In this paper, to model the air transportation system with more ...accuracy, from physical facilities to traffic applications, three-layer networks, including the air route network, the city-pair airline network, and flight operation network, are built, where the air route network is regarded as the physical layer, and city-pair airline network and flight operation network are the application layers. Furthermore, a powerful tool, complex network theory, is applied to discuss the topology characteristics of the three-layer networks. Moreover, considering the path diversity of city-pair airlines, a simulated annealing-based framework is proposed to optimize the routing paths on an air route network for each city-pair airline, such that the traffic congestion of the air route network can be alleviated, where an elaborated method for perturbing solutions, named Selection after Remove (SAR), is adopted. Experimental results show that, compared with the default routing paths, the shortest routing paths, and the random routing paths, the proposed routing-path optimization strategy can reduce the maximum traffic flows of the air route network by 2.4%, 4.6%, and 4.8%, respectively, which shows that the proposed optimization method performs well in alleviating the traffic congestion of the air route network.
Uniformly and controllably introducing oxygen vacancy (Ov) into spinel electrocatalysts is still a great challenge for the oxygen evolution reaction (OER). Herein, we demonstrate the synthesis of ...spinel Co3O4 mesoporous nanosheets aggregation with tunable Ov by a simple phosphorus (P) doping strategy. It is found that a trade-off between Ov and electronic conductivity plays an important role in improving OER electrocatalytic activity. The optimized Co3O4-xP0.15 electrocatalyst delivers a current density of 20 mA cm−2 in alkaline media within a small overpotential of only 338 mV, which is much lower than the corresponding Co3O4 (395 mV) and the commercial RuO2 (368 mV) catalysts. The Tafel slope is 52 mV dec−1 and the overpotential gives negligible increase even through 8 h OER at 10 mA cm−2. The superior OER catalytic activity is mainly attributed to the 2D mesoporous nanosheets (rich active sites) and appropriate Ov (fast electrons transfer). This work provides a simple and effective strategy to control Ov concentration in spinel electrocatalysts for enhancing water oxidation capability.
Display omitted
•The oxygen vacancy can be controlled by a P-doping strategy.•The mesoporous Co3O4-xPy nanosheet enriches electrocatalytic active sites.•The optimized Co3O4-xP0.15 catalysts show superior OER activity and durability.
PDF
