Ultra-low Pt ordered cathodes confront low activity and water flooding owing to inadequate triple-phase-boundaries (TPBs). We infiltrate perfluorosulfonic acid dispersion into PtZn@Ptskin porous nanotubular array (PNA) with a thickness of 290 ± 40 nm and 54.8 ± 0.5 µgPt cm-2, thus fully coating it with resin layer up to 3 nm to nanoengineer TPBs. The PNA cathode demonstrates the highest power density of 12.55 W mgPt-1 in the literature. Besides electrochemically active surface area of 23.2 m2 gPt-1 and mass activity of 0.68 A mgPt-1, TPBs enable 39.0% improvement in R_(O_2)^(non-Fick) relative to Pt/C cathode. 19.9 ± 4.7 nm tubular interiors and 2.0 ± 0.6 nm pores in tubular wall are beneficial for O2 Knudsen diffusion. Molecular dynamics simulations (MD) indicate that TPBs offer 2.8-fold improvement in local O2 permeation and weaken van der Waals, rendering the PNA cathode to perform at 1 A cm-2 for 60 h without flooding.

IrRu nanoparticles surrounded by Ir/Ru–N–C exhibit high CO tolerance arising from CO removal via the following reaction: CO ad –IrRu nanoparticle + OH ad –Ir/Ru–N–C → COOH ad .

Proton exchange membrane water electrolysis (PEMWE) is an environmentally friendly and efficient technology for hydrogen production, playing a vital role in mitigating the fossil energy crisis and bridging renewable energy generation with hydrogen utilization. This work investigates an Ir0.5Ru0.5 nanocluster supported on the nitrogen-vacation-rich niobium nitride (Ir0.5Ru0.5/NbN) for acidic oxygen evolution reaction (OER). Through defect engineering, the electron cloud density of Ir0.5Ru0.5 active sites is precisely modulated, thereby reinforcing strong metal-support interaction (SMSI) at interfaces. Concomitantly, Ir0.5Ru0.5 nanoclusters with high-density grain boundaries induce local charge rearrangement and orbital hybridization for precise d-band center downshift, are fabricated via a doping strategy, thereby accelerating the intrinsic reaction kinetics of OER. The Ir0.5Ru0.5/NbN catalyst exhibits excellent OER performance, achieving a low overpotential of 228 mV at 10 mA cm-2 and high stability, maintaining activity for 700 h without degradation. In addition, it presents outstanding performance as an anode in PEMWE with a cell voltage of 1.79 V at 2 A cm-2. This work provides a viable and efficient approach to reduce Ir loading in PEMWE dramatically, offering a prospective strategy for the cost-effective generation of green hydrogen.

New synthetic routes are required to create advanced Fe-N-C electrocatalysts for eventual substitution of commercial Pt/C toward acidic oxygen reduction reaction (ORR). Herein, we report the co-assembly of ORR-active hemin molecule, 2-methylimidazole (2-MI), and ZnII acetate to achieve single-molecule hemin locked in the nanocages of zeolite imidazolate framework-8 (ZIF-8). Density functional theory (DFT) and spectroscopic analysis show that coordination, H-bond and it-it interaction exist between ZIF-8 cage and hemin, which allow ZIF-8 nanocages to plentifully encapsulate and anchor distorted and shrunk single-molecule hemin. After pyrolysis, the resultant HD-Fe-N-C has 4.5 wt% of atomically dispersed Fe and exhibits excellent activity in terms of a half-wave potential (E1/2) of 0.856 V (vs. RHE) toward ORR, closely approaching that of commercial Pt/C (0.871 V vs. RHE). Furthermore, DFT indicates that the active sites of HD-Fe-N-C in the form of OH-FeIIIN4C12 and OH-FeIIIN2+2C10 have lowered Gibbs free energy for ORR rate determining step (H++*OH + e- -> H2O) relative to that of regular FeIIN4C12 and FeIIN2+2C10. Additionally, HD-Fe-N-C demonstrates an improved durability with 27 mV of E1/2 decay, superior to that of commercial Pt/C (29 mV). DFT and H2O2 decomposition experiments indicate that the excellent durability of HD-Fe-N-C is on account of suppressing the production of H2O2.

The key requirement for applying anion exchange membranes (AEMs) in water electrolyzers and fuel cells is the concurrent enhancement of hydroxide conductivity and alkaline stability. To this end, we herein report a novel hexa-arm branched poly (aryl piperidinium) AEM incorporating bulky three-dimensional tris (4-carbazol-9-ylphenyl) amine (TCA) unit. The TCA unit creates a high-density ion conduction network via increased free volume and promoted microphase separation, while its steric hindrance effect protects the piperidinium cations from hydroxide attack. With a TCA content of 3%, the fabricated membrane (ion exchange capacity being 2.75 mmol g-1) achieves an OH- conductivity of 155.7 mS cm-1 at 80°C and retains 95.1% conductivity after 2000 h in 1 M NaOH at 80°C. When assembled into a fuel cell, it delivers a peak power density of 1.95 W cm-2 at 80°C under 1.3 bar back pressure; in a water electrolyzer operating at 80°C, it yields a current density of 9.51 A cm-2 at 2.0 V. This study offers a novel branching strategy to improve ion transport in AEMs and demonstrates how the branching degree influences alkaline stability of the membrane, which is useful for further improvement of the membrane and device performances.

Identifying new cathode materials with excellent properties is crucial for improving the overall energy-storage performance of aqueous zinc-ion batteries (AZIBs). Vanadium-based materials with superior theoretical specific capacities are the main candidates for cathode materials in AZIBs; however, their slow kinetics and poor stability limit their application. Hence, we prepared K0.19V2O5 0.68H2O (KVOH) nanorods with mixed valence states by pre-inserting K+ into V2O5 to enhance the structural stability and electrical conductivity. The K+ in the interlayer altered the electronic structure and formed stable K-O bonds, constructing a 3D electron conduction network. Oxygen vacancies provided extra active sites for Zn2+, increased the surface reactivity to enhance Zn2+ storage capacity, and inhibited the dissolution of the electrode material in the electrolyte. The specific capacity of the KVOH cathode reached 479.4 mAh g-1 at 0.1 A g-1, with a 92.5% capacity retention after 10 000 cycles at 8 A g-1. Overall, this study provides a general strategy for designing and integrating cathode materials that achieve both high capacity and high-rate performance, paving the way for advancements in the field of AZIBs.

RuAgW/C demonstrates an excellent mass specific exchange current density (j0,m) of 442.9 A gRu-1 superior to that of Pt/C (329.7 A gPt-1) toward the alkaline hydrogen oxidation reaction (HOR) primarily owing to weakened hydrogen binding energy (HBE) and strengthened hydroxide binding energy (OHBE).

The efficiency of the oxygen reduction reaction (ORR) is limited by the scaling relationship in the conventional oxygen associative pathway. To break such limitations, we present an approach to effectively activate the oxygen dissociative pathway through co-confining single p-block (In, Sn, Pb) atoms and interstitial H atoms within Pd metallenes, leading to good ORR performance. PdPbHx metallenes exhibit a high mass activity of 1.36 A mg-1 at 0.95 V (vs. RHE), which is 46.9 times higher than that of the benchmark Pt/C. The minimal performance decay after 50,000 potential cycles confirms a good stability. In situ vibrational spectroscopy investigations and theoretical calculations highlight that interstitial H atoms facilitate the direct dissociation of O2 while single Pb atoms enhance O2 adsorption strength. The electroactive PdPbHx metallenes is attributed to the up-shifted Pd-4d orbitals induced by H and Pb atoms. This research supplies critical inspiration for developing highly efficient ORR electrocatalysts.

Design and synthesis of highly active and durable bifunctional electrocatalysts is crucial toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in unitized regenerative proton exchange membrane fuel cells (UR-PEMFCs). Herein, we report a simple phase-transfer reduction method to synthesize PtIr nanoparticles with different molar ratios. When the Pt/Ir molar ratio is 2.2:1, the bifunctional oxygen activity is optimal. The ORR mass activity of Pt2.2Ir nanoparticles is 190.3 mA/mgPt @ 0.9 V (vs. RHE), which is 1.8 times and 3.7 times those of commercial Pt black and physically mixed commercial Pt and Ir black (Pt+Ir black), respectively. At the potential of 1.53 V vs. RHE, the OER mass activity of Pt2.2Ir nanoparticles is 202.7 mA/mgIr, which is 2.0 times and 1.3 times those of Ir black and Pt+Ir black, respectively. An overpotential gap of Pt2.2Ir nanoparticles (618 mV) between the half-wave potential of ORR and the potential at 10 mA/cm2 of OER is superior to Pt+Ir black (662 mV). After durability tests, the ORR/OER activity of Pt2.2Ir nanoparticles remained much better than Pt+Ir black. X-Ray photoelectron spectroscopy suggests that the electronic interaction between Pt and Ir accounts for enhanced bifunctional oxygen activity. Eventually, the Pt2.2Ir nanoparticles were evaluated in UR-PEMFCs.

Nonprecious transition metal (TM)-based materials have demonstrated tremendous potential as efficient oxygen reduction reaction (ORR) electrocatalysts. However, establishing reliable relationships between geometric/electronic structures and ORR performances remains a great challenge to design and manufacture high-performance ORR catalysts. In this study, we proposed and validated that reducing the symmetry of the coordination structure of TMs enhanced d-pi interactions, thereby strengthening their adsorption for key intermediates. Then we managed the tuning of the metal center's spin state by substituents, further optimizing the ORR performance. Such advancements were attributed to the orientation differences in d-orbital interactions as a result of asymmetric electronic structure. Based on the understanding of such structure-activity relationships, we designed a covalent organic framework-(COF) based ORR electrocatalyst, which exhibited high activity, rapid kinetic response, and high four-electron transfer selectivity. This work validates an alternative strategy for enhanced ORR through the management of d-pi interactions utilizing asymmetric coordination structures. It inspires the design of TM-based electrocatalysts by providing mechanistic insights into the precise control of the microchemical environments at TM active centers.

High catalyst cost impedes PEM fuel cell (PEMFC) commercialization, making the development of highperformance non-platinum(Pt) group metal (PGM) cathode catalyst layers (CLs) critical for advancing fuel cell technology. CLs contribute to a major portion of PEMFCs cost due to the use of PGM catalysts. To reduce the cost, non-PGM catalysts offer a viable alternative to low-Pt loading. In this study, we develop a three-dimensional (3D) model to investigate the reaction rate, oxygen, and liquid water distributions in PEMFCs with a focus on the non-PGM cathode catalyst layer, which provides unique insights into electrochemically coupled transport processes that cannot be resolved by reduced-dimension or experimental approaches. Experiments were conducted using two types of non-PGM catalysts, including Fe-N-C and Mn-N-C based materials, to validate the 3-D model predictions. It is shown that CL properties such as catalyst materials, porosity, and ionomer content can play important roles in PEMFCs voltage gain, highlighting the performance impact of non-PGM catalysts. Large variations in the liquid water and oxygen contents occur in the gas diffusion layer from the land to channel under 1 A/cm2. The through-plane distributions under the channel show large spatial variations across the non-PGM CLs in oxygen and the electrolyte phase potential. Liquid water shows little change across the catalyst layer based on the 3-D model prediction. These findings advance PEMFC development by informing the design of durable, high-performance non-PGM CLs to reduce fuel cell cost for transportation applications.

The substitution of platinum with low-cost ruthenium is of interest toward alkaline hydrogen oxidation reaction (HOR). However, Ru-based HOR electrocatalysts confront the hurdles of ruthenium oxidation, low activity and CO poisoning. Herein, we report the synthesis of 2-3 nm PdRuMo alloy particles evenly distributed on carbon, followed by in situ evolution into PdHxRuMo/C owning to the formation of surface PdHx in the presence of H2. Remarkably, PdRuMo/C remains stable up to 0.78 V vs. RHE during HOR process in that Ru accepts electrons from Mo and Pd, and H species spills over to protect Ru from being oxidized. To the best of knowledge, PdRuMo/ C possesses the widest potential-stable window among Ru-based HOR electrocatalysts. In addition, PdRuMo/C exhibits an exceptional activity in terms of mass specific exchange current density of 849.6 A gmetal alkaline HOR, which is 2.6 and 3.0 times of that of commercial Pt/C and Ru/C, respectively. The excellent HOR activity originates from high electrochemically active surface area (164.9 m2 gmetal-1 ), surface low-coordination atoms, and strengthened hydroxide binding energy as well as weakened hydrogen binding energy. Furthermore, PdRuMo/C remains 97.2 % of the initial current density in the presence of 1000 ppm CO superior to that of commercial Pt/C (77.7 %) and Ru/C (88.5 %). The remarkable CO-resistance is correlated with weakened CO adsorption as evidenced by negatively shifted CO-stripping peak and d-band center downshift of 0.35 eV. Density functional theory (DFT) further deepens the understanding on the origins of HOR potential stability, activity, reaction mechanism, and CO-resistance of PdRuMo/C. Finally, the high HOR activity of PdRuMo/C was verified in AEMFCs with a peak power density of 344.4 mW cm- 2.

Highly active and durable Fe-N-C electrocatalysts toward acidic oxygen reduction reaction (ORR) remain challenging due to their inferior intrinsic activity, low density, and insufficient exposure of active sites. Herein, we report the pyrolysis of coassembled hemin and copolymer capping on Zn(OH)2 nanosucculent plants, leading to the synthesis of highly porous ultrathin carbon nanoshells comprised of rich atomically dispersed Fe-N-C sites. The nanoshell is about 5.5 +/- 0.8 nm thick with a pore volume of 0.5 cm3 g-1, allowing sufficient exposure of active sites. The nanoshell shows a remarkable ORR half-wave potential (E 1/2) of 0.871 V (vs a reversible hydrogen electrode, RHE). The activity originates from the highest intrinsic activity with a turnover frequency of 11.7 e- site-1 s-1 at 0.8 V (vs RHE) and abundant accessible active sites (2.37 x 1020 g-1). Density functional theory elucidates that the presence of about 4 & Aring; micropores neighboring to Fe-N-C lowers the Gibbs free energy of the ORR rate-determining step (O* + H+ + e- = OH*), which is beneficial for the improvement of intrinsic activity. Moreover, the nanoshell demonstrates a durability with 36 mV of E 1/2 decay superior to that of commercial Pt/C (47 mV) during accelerated durability tests. Eventually, the remarkable activity was embodied by a peak power density of 450.6 mW cm-2 in H2-air single cells.

A challenge faced by quinone polymers for application in flexible solid-state Zn-ion batteries (FSZIBs) is how to design and fabricate their flexible free-standing electrodes with high capacity and excellent cycling stability. Here, a two-step engineering strategy including fabrication of polymer nanowire and construction of sandwichstructured film was developed to achieve a flexible freestanding film based on sulfur heterocyclic quinone polymer (SHQP) for FSZIBs. A core/sheath structured carbon nanotube@SHQP(CNT@SHQP) nanowire was first synthesized by the interfacial polymerization method, in which the it-it interaction between SHQP and CNT promoted the self-assembly of SHQP to form thin nanolayers around CNT. This unique nanostructure was effective in increasing active sites, accelerating electron transfer, shortening the diffusion path of Zn2+ ions, buffering the volume variation while simultaneously enhancing the structural stability of SHQP nanolayers. More importantly, a sandwich-like hierarchical film of reduced graphene oxide|CNT@SHQP|reduced graphene oxide (rGO|CNT@SHQP|rGO) was designed and fabricated using CNT@SHQP nanowires and GO nanosheets through vacuum filtration and further mild reduction. The flexible Zn//rGO|CNT@SHQP|rGO battery exhibited a high capacity (139.9 mA h g- 1 at 0.1 A g- 1) and long-term cycling stability (76.2 % of the initial capacity after 2000 cycles at 1 A g- 1). This strategy can be further extended for fabricating flexible free-standing films of other quinone polymers, which have great potential application in wearable electronics.

Ordered cathodes of proton exchange membrane fuel cells (PEMFCs) suffer the lack of triple-phase boundaries (TPBs) and polarization loss. We report the fabrication of PtZn@Ptskin porous nanotubular array (PNA) with infiltrated polytetrafluoroethylene (PTFE) to nanoengineer TPBs suitable for efficient O2 transfer, proton conduction, electron conduction, as well as water drainage. The PTFE-PtZn@Ptskin PNA is 290 +/- 50 nm thick at 62.0 +/- 1.0 mu gPt cm-2 and 3.9 +/- 1.0 mu gZn cm-2. The PNA exhibits 12.7%, 32.8%, and 82.1% of improved Ohmic, activation, and O2 transfer polarizations relative to regular Pt/C cathode at 1 A cm-2, respectively. For Ohmic polarization, the PNA falls within Debye length, where a strong electric field allows fast proton conduction with the aid of shortened and straightforward pathway along the PNA. For activation polarization, density functional theory (DFT) indicates that the d-band center of PtZn@Ptskin downshifts and weakens O* adsorption relative to Pt, thus boosting the activity of oxygen reduction reaction (ORR). For O2 transfer polarization, molecular dynamics (MD) simulations indicate that PTFE weakens hydrogen bond network and van der Waals force and mitigates water residence time at the interface of PTFE-PtZn@Ptskin/water, leading to 9-fold increase in local O2 concentration.

Proton exchange membrane water electrolyzers (PEMWEs) confront the grand challenge of sluggish kinetics of oxygen evolution reaction (OER). Herein, we present the synthesis of ultrafine 1-2 nm Ir particles on sea urchin-like PdCu (Ir0.58/Pd1.9Cu) via wet chemical reduction of PdCl42-and Cu2+, followed by simple displacement of PdHx by Ir3+ with the aid of HCOOH. Ir0.58/Pd1.9Cu exhibits an overpotential of 191 mV at 10 mA/cm2 superior to that of commercial Ir black (262 mV) toward acidic OER. The electrochemically active surface area of Ir0.58/Pd1.9Cu (850.6 m2/g) is much higher than that of commercial Ir black (411.9 m2/g), and should be a major contributor to the high OER activity. The electronic interaction between PdCu and Ir nanoparticles well tunes the electronic structure of Ir, possibly conferring Ir0.58/ Pd1.9Cu with high activity. Furthermore, density functional theory reveals that the OER rate-determining step (*O / *OOH) on Ir/PdCu has a lowered energy barrier of 0.33 eV compared with that of Ir, beneficial for the high OER activity. Additionally, Ir0.58/Pd1.9Cu demonstrates a reasonably good stability during 20 h of chronopotentiometry test, superior to that of commercial Ir black. Finally, the high OER activity of Ir0.58/Pd1.9Cu was verified in a PEMWE. (c) 2023 Elsevier Ltd. All rights reserved.

Electrochemical CO2 reduction reaction (CO2RR) is an attractive approach for the mitigation of CO2 emissions and the production of value-added chemicals. However, it remains a challenge to achieve high selectivity of desirable C2 products like ethylene (C2H4) with high economic value and large market. Herein, we report the fabrication of unprecedented Cu(OH)2 nanochrysanthemums catalyst layer (CL). Interestingly, Cu(OH)2 nanochrysanthemums CL exhibits a C2H4 Faradaic efficiency (FE) of 51.2 ± 0.5% and a FE(C2H4+C2H5OH) of 70.0 ± 0.5% in pH nearly neutral electrolytes. It is worth mentioning that Cu(OH)2 nanochrysanthemums CL achieves the highest FEC2 among documented Cu(OH)2 electrocatalysts. The high FEC2H4 and FEC2 can be attributed to the high electrochemical surface area (ECSA, 21.9 mF cm-2) of Cu(OH)2 nanochrysanthemums. In addition, the well balanced hydrophilicity-hydrophobicity of the Cu(OH)2 nanochrysanthemums CL also contributes to the high FEC2H4 and FEC2 by simultaneously satisfying efficient transfer of hydrophobic CO2 and C2H4 as well as hydrophilic H2O and C2H5OH. COMSOL multiphysics simulations and density functional theory (DFT) calculations further suggest that the negatively charged sharp tips of Cu(OH)2 nanochrysanthemums would trigger the accumulation of K+ and offer strong local electric field of 9.8 V μm-1, promoting C-C coupling and suppressing hydrogen evolution reaction (HER).

Hydrogen evolution reaction and hydrogen oxidation reaction (HER/HOR) are two key reactions in the electrolysis of water to produce green hydrogen and fuel cells, respectively. However, the slow kinetics of HER/HOR under alkaline conditions and lack of catalysts with good activity and durability limit their development and application. Here, Pd nanoparticles supported by CeO2/C with abundant oxygen vacancies were synthesized for alkaline HER/HOR. The results of physical characterizations and electrochemical measurements indicated that small-size Pd nanoparticles were in full contact with CeO2, and charge transfer occurred at the Pd-CeO2 interface. The rich Pd-CeO2 interface and the interaction between metal and metal oxide carriers greatly improved the electrocatalytic activity of HER and HOR under alkaline conditions. The optimal Pd/CeO2/C exhibited excellent HER/HOR activity with a higher HER exchange current density (1.963 mA cm(-2)) than commercial Pt/C. Furthermore, the HER and HOR mass activity of Pd/CeO2/C reached 33 times and 9.2 times that of Pd/C, respectively. Pd/CeO2/C exhibited enhanced electrocatalytic stability due to the anchoring of Pd via abundant oxygen vacancy defects in CeO2/C. This work provides a meaningful reference for the rational regulation of metal-support interfaces and the application of metal-oxide-support-based electrocatalysts in electrocatalytic reactions.

Catalyst coated membrane (CCM) is the core component of proton exchange membrane water electrolyzers (PEMWEs) and confronts the challenge of unaffordable Ir loading of 2-4 mg cm-2, polarization loss and inferior stability closely correlated with low-activity disordered thick catalyst layers (CLs, 3-10 mu m) frequently fabricated by catalyst ink painting. We report wet-chemical direct growth of semi-ordered PtIr nanoflowers array as CLs on both sides of membrane, leading to an integrated ultra-low PtIr CCM (IUCCM) with a single-side PtIr loading of 62.7 mu g (1.8 mu g Pt+60.9 mu g Ir) cm- 2 and a CL thickness of 429.1 +/- 62.9 nm. Remarkably, the IUCCM exhibits 20.8 %, 34.8 % and 23.8 % attenuation of activation, ohmic and mass transfer polarization relative to a house-made CCM, respectively, and a current density of 2 A cm-2 at 1.77 V as well as the highest specific power of 21.5 kW gIr- 1 at 1.6 V in the literature. The improvement of activation polarization is primarily arising from the electronic effect between Pt and Ir as evidenced by the d-band center downshift of 0.80 eV. The thin and semiordered CL largely accounts for the mitigation of mass transfer and ohmic polarization. Notably, the IUCCM displays a good long-term stability with a degradation rate of ca. 44.4 mu V h-1 during 300 h of electrolysis at 0.5 A cm-2. The superior stability can be attributed to strong CL/membrane interfacial interaction with the CL rooted down into the membrane matrix analogous to teeth as well as structural robustness of PtIr CL.

Direct ascorbic acid fuel cells (DAAFCs) employ biocompatible ascorbic acid (AA) as fuel, allowing convenient storage, transportation, and fueling as well as avoiding fuel crossover. The AA oxidation reaction (AAOR) largely governs the performance of DAAFCs. However, AAOR electrocatalysts currently have low activity, and state-of-the-art ones are limited to carbon black. Herein, we report the synthesis of an unprecedented AAOR electrocatalyst comprising 3.9 ± 1.1 nm CeO2 nanoparticles evenly distributed on carbon black simply by the wet chemical precipitation of Ce(OH)3 and a subsequent heat treatment. The resultant CeO2/C shows a remarkable AAOR activity with a peak current density of 13.1 mA cm−2, which is 1.7 times of that of carbon black (7.67 mA cm−2). According to X-ray photoelectron spectroscopy (XPS), the surface Ce3+ of CeO2 appears to contribute to the AAOR activity. Furthermore, our density functional theory (DFT) calculation reveals that that the proton of the hydroxyl group of AA can easily migrate to the bridging O sites of CeO2, resulting in a faster AAOR with respect to the pristine carbon, -COOH, and -C=O sites of carbon. After an i-t test, CeO2/C loses 17.8% of its initial current density, which is much superior to that of carbon black. CeO2 can capture the electrons generated by the AAOR to protect the -COOH and -C=O sites from being reduced. Finally, DAAFCs fabricated with CeO2/C exhibit a remarkable power density of 41.3 mW cm−2, which is the highest among proton-exchange-membrane-based DAAFCs in the literature.