Hydrogen economy is imagined where excess electric energy from renewable sources stored directly by electrochemical water splitting into hydrogen is later used as clean hydrogen fuel. ...Electrocatalysts with the superhigh current density (1000 mA cm−2‐level) and long‐term durability (over 1000 h), especially at low overpotentials (<300 mV), seem extremely critical for green hydrogen from experiment to industrialization. Along the way, numerous innovative ideas are proposed to design high efficiency electrocatalysts in line with industrial requirements, which also stimulates the understanding of the mass/charge transfer and mechanical stability during the electrochemical process. It is of great necessity to summarize and sort out the accumulating knowledge in time for the development of laboratory to commercial use in this promising field. This review begins with examining the theoretical principles of achieving high‐efficiency electrocatalysts with high current densities and excellent durability. Special attention is paid to acquaint efficient strategies to design perfect electrocatalysts including atomic structure regulation for electrical conductivity and reaction energy barrier, array configuration constructing for mass transfer process, and multiscale coupling for high mechanical strength. Finally, the importance and the personal perspective on future opportunities and challenges, is highlighted.
This review begins with examining the theoretical principles of achieving high‐efficiency electrocatalysts with large current densities and excellent durability. Special attention of this review is paid to acquaint efficient strategies to design satisfactory electrocatalysts including atomic structure regulation for electrical conductivity and reaction energy barrier, array configuration constructing for mass transfer process, and multiscale coupling for high mechanical strength.
Electrochemical synthesis based on electrons as reagents provides a broad prospect for commodity chemical manufacturing. A direct one‐step route for the electrooxidation of amino C−N bonds to nitrile ...C≡N bonds offers an alternative pathway for nitrile production. However, this route has not been fully explored with respect to either the chemical bond reforming process or the performance optimization. Proposed here is a model of vacancy‐rich Ni(OH)2 atomic layers for studying the performance relationship with respect to structure. Theoretical calculations show the vacancy‐induced local electropositive sites chemisorb the N atom with a lone pair of electrons and then attack the corresponding N(sp3)−H, thus accelerating amino C−N bond activation for dehydrogenation directly into the C≡N bond. Vacancy‐rich nanosheets exhibit up to 96.5 % propionitrile selectivity at a moderate potential of 1.38 V. These findings can lead to a new pathway for facilitating catalytic reactions in the chemicals industry.
Vacancy‐rich Ni(OH)2 nanosheets are proposed to realize a direct one‐step route for the electrooxidation of amino C−N bonds to nitrile C≡N bonds for nitrile production. During the catalytic reaction the local vacancy‐induced electropositive site chemisorbs the N atom with a lone pair of electrons and then attacks the corresponding N−H bond.
Activating basal plane inert sites will endow MoTe
2
with prominent hydrogen evolution reaction (HER) catalytic capability and arouse a new family of HER catalysts. Herein, we fabricated single MoTe
...2
sheet electrocatalytic microdevice for
in situ
revealing the activated basal plane sites by vacancies introducing. Through the extraction of electrical parameters of single MoTe
2
sheet, the in-plane and interlayer conductivities were optimized effectively by Te vacancies due to the defect levels. More deeply, Te vacancies can induce the delocalization of electrons around Mo atoms and shift the d-band center, as a consequence, facilitate the adsorption of H from the catalyst surface for HER catalysis. Benefiting by the coordinated regulation of band structure and local charge density, the overpotential at −10 mA·cm
−
2
was reduced to 0.32 V after Te vacancies compared to 0.41 V for the basal plane sites of same MoTe
2
nanosheet. Meanwhile, the insights gained from single nanosheet electrocatalytic microdevice can be applied to the improved HER of the commercial MoTe
2
power. That the
in situ
testing of the atomic structure-electrical behavior-electrochemical properties of a single nanosheet before/after vacancies introducing provides reliable insight to structure-activity relationships.
The reaction interface which governs the electrocatalytic behavior is notoriously hard to understand due to inadequate regulatory and detection methods. By using on-chip microdevices, we employ ...variable back-gate voltages to generate molecular polarization and thus fine-tune the concentration of hydronium ions (H
3
O
+
) in electrochemical double layers for efficient hydrogen evolution. Taking C
60
/ MoS
2
heterojunction as a prototype, electrical tests reveal that the back-gate promotes the charge transfer from C
60
to MoS
2
, leading to the polarization of C
60
.
In situ
photoluminescence spectra verify that the polarized C
60
can attract H
3
O
+
to accumulate in the vicinity of MoS
2
in the external electric field. Profiting from the back-gated H
3
O
+
enrichment, the hydrogen evolution current is increased by five times at −0.45 V
RHE
when a 1.5-V back-gate voltage is applied. The insight into the reaction interface from manipulation to detection can facilitate diverse catalytic reactions.
Tandem catalysts can divide the reaction into distinct steps by local multiple sites and thus are attractive to trigger CO2RR to C2+ products. However, the evolution of catalysts generally exists ...during CO2RR, thus a closer investigation of the reconstitution, interplay, and active origin of dual components in tandem catalysts is warranted. Here, taking AgI−CuO as a conceptual tandem catalyst, we uncovered the interaction of two phases during the electrochemical reconstruction. Multiple operando techniques unraveled that in situ iodine ions leaching from AgI restrained the entire reduction of CuO to acquire stable active Cu0/Cu+ species during the CO2RR. This way, the residual iodine species of the Ag matrix accelerated CO generation and iodine‐induced Cu0/Cu+ promotes C−C coupling. This self‐adaptive dual‐optimization endowed our catalysts with an excellent C2+ Faradaic efficiency of 68.9 %. Material operando changes in this work offer a new approach for manipulating active species towards enhancing C2+ products.
The interplay of dual components in tandem catalysts is uncovered and utilized during the electrochemical reconstruction for promoting CO2 electroreduction to C2+ products. Taking AgI−CuO as a conceptual tandem catalyst, in situ iodine ions leaching from AgI restrain the entire reduction of CuO to acquire stable active Cu0/Cu+ species, thus achieving a high C2+ Faradaic efficiency of 68.9 %.
Engineering the reaction interface is necessary for advancing various electrocatalytic processes. However, most designed catalysts tend to be ineffective due to the inevitable structural ...reconstruction. Here we utilize that operando electrocatalysis variations (i.e., chalcogen leaching) manipulate the reactant interface toward amine electrooxidation. Taking chalcogen-doped Ni(OH)2 as an example, operando techniques uncover that chalcogens leach from the matrix and then adsorb on the surface of NiOOH as chalcogenates during the electrooxidation process. The charged chalcogenates will induce the local electric field that pushes the polar amines through the inner Helmholtz plane to enrich on the catalyst surface. Meanwhile, the polarization effect of chalcogenates and amines boost amino C–N bond activation for dehydrogenation into nitrile CN bonds. Under the promotion effect of surface-adsorbed chalcogenate ions, our catalysts display over 99.5% propionitrile selectivity at the low potential of 1.317 V with an ultrahigh current density. This finding highlights the use of operando changes of catalysts to rationally design efficient catalysts and further clarifies the underlying role of chalcogen atoms in the electrooxidation process.
Manipulating the catalyst–electrolyte interface to push reactants into the inner Helmholtz plane (IHP) is highly desirable for efficient electrocatalysts, however, it has rarely been implemented due ...to the elusive electrochemical IHP and inherent inert catalyst surface. Here, we propose the introduction of local force fields by the surface hydroxyl group to engineer the electrochemical microenvironment and enhance alkaline hydrogen evolution activity. Taking a hydroxyl group immobilized Ni/Ni3C heterostructure as a prototype, we reveal that the local hydrogen bond induced by the surface hydroxyl group drags 4‐coordinated hydrogen‐bonded H2O molecules across the IHP to become free H2O and thus continuously supply reactants forcatalytic sites catalytic sites. In addition, the hydroxyl group coupled with the Ni/Ni3C heterostructure further lowers the water dissociation energy by polarization effects. As a direct outcome, hydroxyl‐rich catalysts surpass Pt/C activity at high current density (500 mA cm−2 @ ≈276 mV) in alkaline medium.
Taking a hydroxyl group immobilized Ni/Ni3C heterostructure as a prototype, the introduction of a local hydrogen bond force field at the catalyst–electrolyte interface is proposed to create a free H2O molecule enriched microenvironment near the inner Helmholtz plane. Continuous replenishment of free H2O molecules for the catalytic site achieved highly alkaline hydrogen evolution reaction (HER) activity (500 mA cm−2 @ ≈276 mV), outperforming Pt/C catalysts.
Nickel-iron layered double hydroxides (NiFe LDHs) represent a promising candidate for oxygen evolution reaction (OER), however, are still confronted with insufficient activity, due to the slow ...kinetics of electrooxidation of Ni
2+
cations for the high-valent active sites. Herein, nanopore-rich NiFe LDH (PR-NiFe LDH) nanosheets were proposed for enhancing the OER activity together with stability. In the designed catalyst, the confined nanopores create abundant unsaturated Ni sites at edges, and decrease the migration distance of protons down to the scale of their mean free path, thus promoting the formation of high-valent Ni
3+/4+
active sites. The unique configuration further improves the OER stability by releasing the lattice stress and accelerating the neutralization of the local acidity during the phase transformation. Thus, the optimized PR-NiFe LDH catalysts exhibit an ultralow overpotential of 278 mV at 10 mA·cm
−2
and a small Tafel slope of 75 mV·dec
−1
, which are competitive among the advanced LDHs based catalysts. Moreover, the RP-NiFe LDH catalyst was implemented in anion exchange membrane (AEM) water electrolyzer devices and operated steadily at a high catalytic current of 2 A over 80 h. These results demonstrated that PR-NiFe LDH could be a viable candidate for the practical electrolyzer. This concept also provides valuable insights into the design of other catalysts for OER and beyond.
•A stack-level multiphysics model with bubble and shunt current effects is proposed.•The proposed ER curve is applied to quantify various factors on stack performance.•The reduction of single cell ...area will be a trend in size design for on-grid stacks.•The practical scale-up AWE stack coupled with RES is investigated.
Large-capacity hydrogen production systems are crucial for promoting green hydrogen development. However, the scaling-up of electrolysis stacks through larger electrode areas or additional electrodes may increase the bubble coverage effect and shunt current effect, leading to efficiency degradation. Therefore, a quantitative model that considers interrelated factors is needed to optimize the size design during the scaling-up process. This paper presents a stack-level multiphysics model that describes the electrochemical and two-phase flow processes within the stack. The model is validated experimentally, with a relative error of the current–voltage (IV) curve within 4%. Based on the model, the energy efficiency-reaction current density (ER) curves of different stacks are analyzed and used to provide performance optimization strategies for stacks coupled with renewable energy sources (RES). The findings demonstrate that in on-grid mode, the small cell design leads to a hydrogen production rate increase of over 6%, driving a trend towards miniaturization of cell areas. In addition, during off-grid operation, the hydrogen production variations among different designs can exceed 4% due to performance differences under heavy and light loads. Therefore, optimizing electrolyzer performance requires considering power source fluctuations and conducting specialized computational optimizations based on specific scenarios. In summary, this paper proposes optimization strategies of size design for scaling up electrolysis stacks to improve stack performance, with the goal of driving the advancement of green hydrogen.
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