Monosymmetric Fe-N4 sites enabling durable proton exchange membrane fuel cell cathode by chemical vapor modification.

The limited durability of metal-nitrogen-carbon electrocatalysts severely restricts their applicability for the oxygen reduction reaction in proton exchange membrane fuel cells. In this study, we employ the chemical vapor modification method to alter the configuration of active sites from FeN4 to the stable monosymmetric FeN2+N'2, along with enhancing the degree of graphitization in the carbon substrate. This improvement effectively addresses the challenges associated with Fe active center leaching caused by N-group protonation and free radicals attack due to the 2-electron oxygen reduction reaction. The electrocatalyst with neoteric active site exhibited excellent durability. During accelerated aging test, the electrocatalyst exhibited negligible decline in its half-wave potential even after undergoing 200,000 potential cycles. Furthermore, when subjected to operational conditions representative of fuel cell systems, the electrocatalyst displayed remarkable durability, sustaining stable performance for a duration exceeding 248 h. The significant improvement in durability provides highly valuable insights for the practical application of metal-nitrogen-carbon electrocatalysts.

Single atom sites as CO scavenger to allow for crude hydrogen usage in PEMFC.

Nanosized Pt catalysts are the catalyst-of-choice for proton exchange membrane fuel cell (PEMFC) anode, but are limited by their extreme sensitivity to CO in parts per million (ppm) level, thereby making the use of ultrapure H2 a prerequisite to ensure acceptable performance. Herein, we confront the CO poisoning issue by bringing the Ir/Rh single atom sites to synergistically working with their metallic counterparts. In presence of 1000 ppm CO, the catalyst represents not only undisturbed H2 oxidation reaction (HOR) catalytic behavior in electrochemical cell, but also unparalleled peak power density at 643 mW cm-2 in single cell, 27-fold in mass activity of the best PtRu/C catalysts available. Pre-poisoning experiments and surface-enhanced Raman scattering spectroscopy (SERS) and calculation results in combine suggest the presence of adjacent Ir/Rh single atom sites (SASs) to the nanoparticles (NPs) as the origin for this prominent catalytic behavior. The single sites not only exhibit superb CO oxidation performance by themselves, but can also scavenge the CO adsorbed on approximated NPs via supplying reactive OH* species. We open up a new route here to conquer the formidable CO poisoning issue through single atom and nanoparticle synergistic catalysis, and pave the way towards a more robust PEMFC future.

Operando formation of highly efficient electrocatalysts induced by heteroatom leaching.

Heterogeneous nano-electrocatalysts doped with nonmetal atoms have been studied extensively based on the so-called dopant-based active sites, while little attention has been paid to the stability of these dopants under working conditions. In this work, we reveal significantly, when the redox working potential is too low negatively or too high positively, the active sites based on these dopants actually tend to collapse. It means that some previously observed "remarkable catalytic performance" actually originated from some unknown active sites formed in situ. Take the Bi-F for the CO2RR as an example, results show that the observed remarkable activity and stability were not directly from F-based active sites, but the defective Bi sites formed in situ after the dopant leaching. Such a fact is unveiled from several heteroatom-doped nanocatalysts for four typical reactions (CO2RR, HER, ORR, and OER). This work provides insight into the role of dopants in electrocatalysis.

Rare Earth Evoked Subsurface Oxygen Species in Platinum Alloy Catalysts Enable Durable Fuel Cells.

Alleviating the degradation issue of Pt based alloy catalysts, thereby simultaneously achieving high mass activity and high durability in proton exchange membrane fuel cells (PEMFCs), is highly challenging. Herein, we provide a new paradigm to address this issue via delaying the place exchange between adsorbed oxygen species and surface Pt atoms, thereby inhibiting Pt dissolution, through introducing rare earth bonded subsurface oxygen atoms. We have succeeded in introducing Gd-O dipoles into Pt3 Ni via a high temperature entropy-driven process, with direct spectral evidence attained from both soft and hard X-ray absorption spectroscopies. The higher rated power of 0.93 W cm-2 and superior current density of 562.2 mA cm-2 at 0.8 V than DOE target for heavy-duty vehicles in H2 -air mode suggest the great potential of Gd-O-Pt3 Ni towards practical application in heavy-duty transportation. Moreover, the mass activity retention (1.04 A mgPt -1 ) after 40 k cycles accelerated durability tests is even 2.4 times of the initial mass activity goal for DOE 2025 (0.44 A mgPt -1 ), due to the weakened Pt-Oads bond interaction and the delayed place exchange process, via repulsive forces between surface O atoms and those in the sublayer. This work addresses the critical roadblocks to the widespread adoption of PEMFCs.

Intrinsic spin shielding effect in platinum-rare-earth alloy boosts oxygen reduction activity.

Oxygen reduction reactions (ORRs) involve a multistep proton-coupled electron process accompanied by the conversion of the apodictic spin configuration. Understanding the role of spin configurations of metals in the adsorption and desorption of oxygen intermediates during ORRs is critical for the design of efficient ORR catalysts. Herein, a platinum-rare-earth-metal-based alloy catalyst, Pt2Gd, is introduced to reveal the role of spin configurations in the catalytic activity of materials. The catalyst exhibits a unique intrinsic spin reconfiguration because of interactions between the Gd-4f and Pt-5d orbitals. The adsorption and desorption of the oxygen species are optimized by modifying the spin symmetry and electronic structures of the material for increased ORR efficiency. The Pt2Gd alloy exhibits a half-wave potential of 0.95 V and a superior mass activity of 1.5 A·mgPt-1 in a 0.1 M HClO4 electrolyte, as well as higher durability than conventional Pt/C catalysts. Theoretical calculations have proven that the spin shielding effect of Gd pairs increases the spin symmetry of Pt-5d orbitals and adsorption preferences toward spin-polarized intermediates to facilitate ORR. This work clarifies the impact of modulating the intrinsic spin state of Pt through the interaction with the local high spin 4f orbital electrons in rare-earth metals, with the aim of boosting the spin-related oxygen reduction reaction, thus fundamentally contributing to the understanding of new descriptors that control ORR activity.

Customized reaction route for ruthenium oxide towards stabilized water oxidation in high-performance PEM electrolyzers.

The poor stability of Ru-based acidic oxygen evolution (OER) electrocatalysts has greatly hampered their application in polymer electrolyte membrane electrolyzers (PEMWEs). Traditional understanding of performance degradation centered on influence of bias fails in describing the stability trend, calling for deep dive into the essential origin of inactivation. Here we uncover the decisive role of reaction route (including catalytic mechanism and intermediates binding strength) on operational stability of Ru-based catalysts. Using MRuOx (M = Ce4+, Sn4+, Ru4+, Cr4+) solid solution as structure model, we find the reaction route, thereby stability, can be customized by controlling the Ru charge. The screened SnRuOx thus exhibits orders of magnitude lifespan extension. A scalable PEMWE single cell using SnRuOx anode conveys an ever-smallest degradation rate of 53 µV h-1 during a 1300 h operation at 1 A cm-2.

Regulating the MXene-Zinc Interfacial Structure toward a Highly Revisable Metal Anode of Zinc-Air Batteries.

Rechargeable aqueous Zn-air batteries have been regarded as one of the most promising systems for flexible energy storage devices due to their high specific energy, safety, and cost effectiveness. However, Zn metal anodes exposed to strong alkaline electrolytes suffer from several issues such as corrosion, dissolution, and passivation, resulting in extremely poor cycle reversibility. Motivated by this challenge, we herein strategically design an MXene/Zn metal anode interfacial structure with single/few-layer Ti3C2Tx MXene as a protective layer. Such a design not only isolates the direct contact between Zn metal anodes and electrolytes but also inhibits zincate dissolution due to the ion screening function of Ti3C2Tx, potentially addressing the stubborn issues that Zn anodes faced with. As a result, the Ti3C2Tx-protected Zn metal anode exhibits superior cycle stability (stable for more than 400 cycles) to the bare Zn counterpart (20 cycles) at a high current density of 5.0 mA cm-2. When integrated into Zn-air coin cells, it has a high depth of discharge of 91% and operates stably for 140 cycles with small resistance. More interestingly, the excellent flexibility of the as-designed Ti3C2Tx-protected Zn metal anode endows the quasi-solid-state batteries with admirable voltage stability at different bending angles from 0 to 180°.

Challenges and Strategies of Anion Exchange Membranes in Hydrogen-electricity Energy Conversion Devices.

Alkaline hydrogen-electricity energy conversion technologies, involving anion exchange membrane fuel cells (AEMFCs) and anion exchange membrane water electrolyzers (AEMWEs) are more appealing than the acidic counterparts due to the elimination of precious metal catalysts. However, the physicochemical properties of anion exchange membrane (AEMs), i.e., ionic conductivity, mechanical strength, stability, etc., are inferior to that of proton exchange membranes (PEMs), thus hindering these alkaline technologies from practical employment. To promote their development, we summarize the main challenges and the corresponding strategies of AEMs for the application of AEMFCs and AEMWEs in this review. The hydroxide transportation mechanism, ion exchange capacity, hydration and microscopic morphology that are relevant to the ionic conductivity are discussed firstly. Following the ionic conductivity, another obstacle, stability of AEMs is comprehensively described in terms of alkaline stability, mechanical stability and electrochemical stability. Upon integrating into the devices, water management, carbonation effect and membrane-electrode interface that are critical to the cell performance are highlighted as well. This review is anticipated to provide insights into the AEM design for hydrogen-electric energy conversion devices, thus accelerating the widespread commercialization of these promising technologies.

Co-based Catalysts for Selective H2 O2 Electroproduction via 2-electron Oxygen Reduction Reaction.

Electrochemical production of hydrogen peroxide (H2 O2 ) via two-electron oxygen reduction reaction (ORR) process is emerging as a promising alternative method to the conventional anthraquinone process. To realize high-efficiency H2 O2 electrosynthesis, robust and low cost electrocatalysts have been intensively pursued, among which Co-based catalysts attract particular research interests due to the earth-abundance and high selectivity. Here, we provide a comprehensive review on the advancement of Co-based electrocatalyst for H2 O2 electroproduction. The fundamental chemistry of 2-electron ORR is discussed firstly for guiding the rational design of electrocatalysts. Subsequently, the development of Co-based electrocatalysts involving nanoparticles, compounds and single atom catalysts is summarized with the focus on active site identification, structure regulation and mechanism understanding. Moreover, the current challenges and future directions of the Co-based electrocatalysts are briefly summarized in this review.

Enhanced Acidic Water Oxidation by Dynamic Migration of Oxygen Species at the Ir/Nb2 O5-x Catalyst/Support Interfaces.

Catalyst/support interaction plays a vital role in catalysis towards acidic oxygen evolution (OER), and the performance reinforcement is currently interpreted by either strain or electron donation effect. We herein report that these views are insufficient, where the dynamic evolution of the interface under potential bias must be considered. Taking Nb2 O5-x supported iridium (Ir/Nb2 O5-x ) as a model catalyst, we uncovered the dynamic migration of oxygen species between IrOx and Nb2 O5-x during OER. Direct spectroscopic evidence combined with theoretical computation suggests these migrations not only regulate the in situ Ir structure towards boosted activity, but also suppress its over-oxidation via spontaneously delivering excessive oxygen from IrOx to Nb2 O5-x . The optimized Ir/Nb2 O5-x thus demonstrated exceptional performance in scalable water electrolyzers, i.e., only need 1.839 V to attain 3 A cm-2 (surpassing the DOE 2025 target), and no activity decay during a 2000 h test at 2 A cm-2 .

High-Performance RuOx Catalyst with Advanced Mesoporous Structure for Oxygen Evolution Reaction.

Polymer electrolyte membrane water electrolysis (PEMWE) is regarded as one of the most important cornerstone technologies in the upcoming hydrogen society. However, one of the major problems it encounters is its slow oxygen evolution kinetics, which necessitates the use of large amounts of precious metal catalysts to ensure a satisfactory reaction rate. Herein, we have prepared a series of RuOx with porous structures and ultrahigh Ru utilization toward the oxygen evolution reaction. All porous samples exhibit an enhanced catalytic performance compared with commercial RuOx. Particularly, for the RuOx-350 sample, the overpotential to reach 10 mA cm-2 is as low as 225 mV. It has obvious advantages among all reported pure RuO2-based catalysts. Here, a new strategy was raised to construct efficient RuO2 electrocatalysts with outstanding activity and stability for water electrolysis technology.

Nickel Phosphide Coated with Ultrathin Nitrogen-Doped Carbon Shell as a Highly Durable and Active Catalyst towards Hydrogen Evolution Reaction.

Developing non-precious metal catalysts towards hydrogen evolution reaction (HER) is of both high scientific and technical importance for the widespread application of water electrolysis. Herein, Ni2 P nanoparticles coated with a ultrathin N-doped carbon shell were prepared as a highly efficient HER catalyst. Ni2 P@CN exhibits both enhanced catalytic activity and durability in comparison with the carbon-supported Ni2 P counterpart, and represents 100% faradaic yield for HER in an acidic medium. The improved charge transfer of N-doped graphitic carbon shells contributes to the increase in activity. Meanwhile, the carbon shells suppress the aggregation and exfoliation of Ni2 P nanoparticles. As a result, the synergistic role of the N-doped carbon layer confers the Ni2 P cores with boosted activity and stability.

Description of three new species of Gomphomastacinae (Orthoptera: Eumastacoidea) from the east of Qinghai-Tibet plateau, China.

The grasshopper Subfamily Gomphomastacinae (Orthoptera: Acridoidea: Eumastacidae) is widely distributed in the Qinghai-Tibetan Plateau and Central Asia. This paper describes three new species: Ptygomastax nihilsulcus Ge, sp. nov. Phytomastax pentaspinula Ge, sp. nov. and Pentaspinula unispinula Ge, sp. nov. of the subfamily from the eastern Qinghai-Tibetan Plateau, along with an updated identification key of species of the related genera. Detail figures of the body and genitalia of the new species are also provided.

CO-Tolerant PEMFC Anodes Enabled by Synergistic Catalysis between Iridium Single-Atom Sites and Nanoparticles.

Proton-exchange membrane fuel cells (PEMFCs) are limited by their extreme sensitivity to trace-level CO impurities, thus setting a strict requirement for H2 purity and excluding the possibility to directly use cheap crude hydrogen as fuel. Herein, we report a proof-of-concept study, in which a novel catalyst comprising both Ir particles and Ir single-atom sites (IrNP @IrSA -N-C) addresses the CO poisoning issue. The Ir single-atom sites are found not only to be good CO oxidizing sites, but also excel in scavenging the CO molecules adsorbed on Ir particles in close proximity, thereby enabling the Ir particles to reserve partial active sites towards H2 oxidation. The interplay between Ir nanoparticles and Ir single-atom centers confers the catalyst with both excellent H2 oxidation activity (1.19 W cm-2 ) and excellent CO electro-oxidation activity (85 mW cm-2 ) in PEMFCs; the catalyst also tolerates CO in H2 /CO mixture gas at a level that is two times better than that of the current best PtRu/C catalyst.

Proton exchange membrane fuel cells powered with both CO and H2.

The CO electrooxidation is long considered invincible in the proton exchange membrane fuel cell (PEMFC), where even a trace level of CO in H2 seriously poisons the anode catalysts and leads to huge performance decay. Here, we describe a class of atomically dispersed IrRu-N-C anode catalysts capable of oxidizing CO, H2, or a combination of the two. With a small amount of metal (24 µgmetal⋅cm-2) used in the anode, the H2 fuel cell performs its peak power density at 1.43 W⋅cm-2 When operating with pure CO, this catalyst exhibits its maximum current density at 800 mA⋅cm-2, while the Pt/C-based cell ceases to work. We attribute this exceptional catalytic behavior to the interplay between Ir and Ru single-atom centers, where the two sites act in synergy to favorably decompose H2O and to further facilitate CO activation. These findings open up an avenue to conquer the formidable poisoning issue of PEMFCs.

Carbon monoxide powered fuel cell towards H2-onboard purification.

Proton exchange membrane fuel cells (PEMFCs) suffer extreme CO poisoning even at PPM level (<10 ppm), owning to the preferential CO adsorption and the consequential blockage of the catalyst surface. Herein, however, we report that CO itself can become an easily convertible fuel in PEMFC using atomically dispersed Rh catalysts (Rh-N-C). With CO to CO2 conversion initiates at 0 V, pure CO powered fuel cell attains unprecedented power density at 236 mW cm-2, with maximum CO turnover frequency (64.65 s-1, 363 K) far exceeding any chemical or electrochemical catalysts reported. Moreover, this feature enables efficient CO selective removal from H2 gas stream through the PEMFC technique, with CO concentration reduced by one order of magnitude through running only one single cell, while simultaneously harvesting electricity. We attribute such catalytic behavior to the weak CO adsorption and the co-activation of H2O due to the interplay between two adjacent Rh sites.

Preferentially Engineering FeN4 Edge Sites onto Graphitic Nanosheets for Highly Active and Durable Oxygen Electrocatalysis in Rechargeable Zn-Air Batteries.

Single-atom FeN4 sites at the edges of carbon substrates are considered more active for oxygen electrocatalysis than those in plane; however, the conventional high-temperature pyrolysis process does not allow for precisely engineering the location of the active site down to atomic level. Enlightened by theoretical prediction, herein, a self-sacrificed templating approach is developed to obtain edge-enriched FeN4 sites integrated in the highly graphitic nanosheet architecture. The in situ formed Fe clusters are intentionally introduced to catalyze the growth of graphitic carbon, induce porous structure formation, and most importantly, facilitate the preferential anchoring of FeN4 to its close approximation. Due to these attributes, the as-resulted catalyst (denoted as Fe/N-G-SAC) demonstrates unprecedented catalytic activity and stability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) by showing an impressive half-wave potential of 0.89 V for the ORR and a small overpotential of 370 mV at 10 mA cm-2 for the OER. Moreover, the Fe/N-G-SAC cathode displays encouraging performance in a rechargeable Zn-air battery prototype with a low charge-discharge voltage gap of 0.78 V and long-term cyclability for over 240 cycles, outperforming the noble metal benchmarks.

Construction and Regulation of a Surface Protophilic Environment to Enhance Oxygen Reduction Reaction Electrocatalytic Activity.

Pyrolytic transition metal nitrogen-carbon (M-N/C) materials are considered as the most promising alternatives for platinum-based catalysts toward oxygen reduction reaction (ORR). As the proton-coupled electron transfer step in ORR has been proven to be a rate-determining step in the M-N/C catalysts, we envisaged that building a protophilic surface might be helpful to enhance the ORR activity. Herein, a polyaniline decoration strategy was put forward and realized to confer the Fe-N/C catalyst with a surface protophilic environment. A 20 mV positive shift in half-wave potential was observed owing to the enriched interfacial proton concentration, corresponding to a tripled turnover frequency under acidic conditions (from 0.46 to 1.28 e·s-1·sites-1). Our work blazed a new path toward the design of M-N/C ORR catalysts, commencing via the ORR kinetics.

Fundamental understanding of the acidic oxygen evolution reaction: mechanism study and state-of-the-art catalysts.

The oxygen evolution reaction (OER), as the anodic reaction of water electrolysis (WE), suffers greatly from low reaction kinetics and thereby hampers the large-scale application of WE. Seeking active, stable, and cost-effective OER catalysts in acidic media is therefore of great significance. In this perspective, studying the reaction mechanism and exploiting advanced anode catalysts are of equal importance, where the former provides guidance for material structural engineering towards a better catalytic activity. In this review, we first summarize the currently proposed OER catalytic mechanisms, i.e., the adsorbate evolution mechanism (AEM) and lattice oxygen evolution reaction (LOER). Subsequently, we critically review several acidic OER electrocatalysts reported recently, with focus on structure-performance correlation. Finally, a few suggestions on exploring future OER catalysts are proposed.

Bridge Bonded Oxygen Ligands between Approximated FeN4 Sites Confer Catalysts with High ORR Performance.

The applications of the most promising Fe-N-C catalysts are prohibited by their limited intrinsic activities. Manipulating the Fe energy level through anchoring electron-withdrawing ligands is found effective in boosting the catalytic performance. However, such regulation remains elusive as the ligands are only uncontrollably introduced oweing to their energetically unstable nature. Herein, we report a rational manipulation strategy for introducing axial bonded O to the Fe sites, attained through hexa-coordinating Fe with oxygen functional groups in the precursor. Moreover, the O modifier is stabilized by forming the Fe-O-Fe bridge bond, with the approximation of two FeN4 sites. The energy level modulation thus created confers the sites with an intrinsic activity that is over 10 times higher than that of the normal FeN4 site. Our finding opens a novel strategy to manage coordination environments at an atomic level for high activity ORR catalysts.