Advanced Electrocatalysis for Energy and Environmental Sustainability via Water and Nitrogen Reactions

Fine tuning dual active sites in modulating cascade electrocatalytic nitrate reduction over covalent organic framework

Conversion of NO3- to NH3 proceeds stepwise in natural system under two different enzymes involving intermediate NO2-. Artificial electro-driven NO3- reduction also faces the obstacle of low faradaic efficiency due to insufficient utilization of this intermediate. Herein, we demonstrate a bimetallic COF-based electrocatalyst for the cascade catalysis of NO3--to-NO2--to-NH3 for the first time. TpBpy-Cu2Co4 exhibits a significantly improved performance, with an enhancement factor of 1.4-2 compared to monometallic TpBpy-M. The NH3 yield rate achieves 25.6 mg h-1 mgcat.-1 at -0.55 V vs RHE over TpBpy-Cu2Co4, together with excellent faradaic efficiency (93.4 %). This achievement demonstrates cascade catalysis between Co and Cu units, and their distinct roles are investigated through electrochemical experiments and theory calculations. In electrocatalytic process, Cu site facilities *NO3-to-*NO3H step, while the Co site significantly decreases the energy barrier of *NHOH-to-*NH. The present work provides a valuable inspiration in designing efficient catalysts for cascade reaction.

Ce-doped copper oxide and copper vanadate Cu3VO4 hybrid for boosting nitrate electroreduction to ammonia

The electrocatalytic nitrate reduction to ammonia reaction (ENO3RR) holds great potential as a cost-effective method for synthesizing ammonia. This work designed a cerium (Ce) doped Cu2+1O/Cu3VO4 catalyst. The coupling of vanadium-based oxides with Cu2+1O effectively adjusts the catalyst's electronic structure, addressing the inherent issues of limited activity and low conductivity in typical copper-based oxides; moreover, Ce doping generates oxygen vacancies (Ov), providing more active sites and thereby enhancing the ENO3RR performance. The catalyst exhibits superior NH3Faradaic efficiency (93.7 %) with a NH3 yield of 18.905 mg h-1 cm-2at -0.5 V vs. RHE under alkaline conditions. This study provides guidance for the design of highly efficient catalysts for ENO3RR.

Aqueous alternating electrolysis prolongs electrode lifespans under harsh operation conditions

It is vital to explore effective ways for prolonging electrode lifespans under harsh electrolysis conditions, such as high current densities, acid environment, and impure water source. Here we report alternating electrolysis approaches that realize promptly and regularly repair/maintenance and concurrent bubble evolution. Electrode lifespans are improved by co-action of Fe group elemental ions and alkali metal cations, especially a unique Co2+-Na+ combo. A commercial Ni foam sustains ampere-level current densities alternatingly during continuous electrolysis for 93.8 h in an acidic solution, whereas such a Ni foam is completely dissolved in ~2 h for conventional electrolysis conditions. The work not only explores an alternating electrolysis-based system, alkali metal cation-based catalytic systems, and alkali metal cation-based electrodeposition techniques, and beyond, but demonstrates the possibility of prolonged electrolysis by repeated deposition-dissolution processes. With enough adjustable experimental variables, the upper improvement limit in the electrode lifespan would be high.

Seawater electrolysis for fuels and chemicals production: fundamentals, achievements, and perspectives

Seawater electrolysis for the production of fuels and chemicals involved in onshore and offshore plants powered by renewable energies offers a promising avenue and unique advantages for energy and environmental sustainability. Nevertheless, seawater electrolysis presents long-term challenges and issues, such as complex composition, potential side reactions, deposition of and poisoning by microorganisms and metal ions, as well as corrosion, thus hindering the rapid development of seawater electrolysis technology. This review focuses on the production of value-added fuels (hydrogen and beyond) and fine chemicals through seawater electrolysis, as a promising step towards sustainable energy development and carbon neutrality. The principle of seawater electrolysis and related challenges are first introduced, and the redox reaction mechanisms of fuels and chemicals are summarized. Strategies for operating anodes and cathodes including the development and application of chloride- and impurity-resistant electrocatalysts/membranes are reviewed. We comprehensively summarize the production of fuels and chemicals (hydrogen, carbon monoxide, sulfur, ammonia, etc.) at the cathode and anode via seawater electrolysis, and propose other potential strategies for co-producing fine chemicals, even sophisticated and electronic chemicals. Seawater electrolysis can drive the oxidation and upgrading of industrial pollutants or natural organics into value-added chemicals or degrade them into harmless substances, which would be meaningful for environmental protection. Finally, the perspective and prospects are outlined to address the challenges and expand the application of seawater electrolysis.

Tailored Metal-Porphyrin Based Molecular Electrocatalysts for Enhanced Artificial Nitrogen Fixation to Green Ammonia

Electrochemical nitrogen reduction (E-NRR) is one of the most promising approaches to generate green NH3. However, scarce ammonia yields and Faradaic efficiencies (FE) still limit their use on a large scale. Thus, efforts are focusing on different E-NRR catalyst structures and formulations. Among present strategies, molecular electrocatalysts such as metal-porphyrins emerge as an encouraging option due to their planar structures which favor the interaction involving the metal center, responsible for adsorption and activation of nitrogen. Nevertheless, the high hydrophobicity of porphyrins limits the aqueous electrolyte-catalyst interaction lowering yields. This work introduces a new class of metal-porphyrin based catalysts, bearing hydrophilic tris(ethyleneglycol) monomethyl ether chains (metal = Cu(II) and CoII)). Experimental results show that the presence of hydrophilic chains significantly increases ammonia yields and FE, supporting the relevance of fruitful catalyst-electrolyte interactions. This study also investigates the use of hydrophobic branched alkyl chains for comparison, resulting in similar performances with respect to the unsubstituted metal-porphyrin, taken as a reference, further confirming that the appropriate design of electrocatalysts carrying peripheral hydrophilic substituents is able to improve device performances in the generation of green ammonia.

Amorphous MnRuOx Containing Microcrystalline for Enhanced Acidic Oxygen-Evolution Activity and Stability

Compared to Ir, Ru-based catalysts often exhibited higher activity but suffered significant and rapid activity loss during the challenging oxygen evolution reaction (OER) in a corrosive acidic environment. Herein, we developed a hybrid MnRuOx catalyst in which the RuO2 microcrystalline regions serve as a supporting framework, and the amorphous MnRuOx phase fills the microcrystalline interstices. In particular, the MnRuOx-300 catalyst from an annealing temperature of 300 °C contains an optimal amorphous/crystalline heterostructure, providing substantial defects and active sites, facilitating efficient adsorption and conversion of OH-. In addition, the heterostructure leads to a relative increase of the d-band center close to the Fermin level, thus accelerating electron transfer with reduced charge transfer resistance at the active interface between crystalline and amorphous phases during the OER. The catalyst was further thoroughly evaluated under various operating conditions and demonstrated exceptional activity and stability for the OER, representing a promising solution to replace Ir in water electrolyzers.

P-Block Antimony-Copper Single-Atom Alloys for Selective Nitrite Electroreduction to Ammonia

Electrocatalytic reduction of NO2- to NH3 (NO2RR) offers an effective method for alleviating NO2- pollution and generating valuable NH3. Herein, a p-block single-atom alloy, namely, isolated Sb alloyed in a Cu substrate (Sb1Cu), is explored as a durable and high-current-density NO2RR catalyst. As revealed by the theoretical calculations and operando spectroscopic measurements, we demonstrate that Sb1 incorporation can not only hamper the competing hydrogen evolution reaction but also optimize the d-band center of Sb1Cu and intermediate adsorption energies to boost the protonation energetics of NO2--to-NH3 conversion. Consequently, Sb1Cu integrated in a flow cell achieves an outstanding NH3 yield rate of 2529.4 μmol h-1 cm-2 and FENH3 of 95.9% at a high current density of 424.2 mA cm-2, as well as a high durability for 100 h of electrolysis.

Carbon Corrosion Induced by Surface Defects Accelerates Degradation of Platinum/Graphene Catalysts in Oxygen Reduction Reaction

Graphene supported electrocatalysts have demonstrated remarkable catalytic performance for oxygen reduction reaction (ORR). However, their durability and cycling performance are greatly limited by Oswald ripening of platinum (Pt) and graphene support corrosion. Moreover, comprehensive studies on the mechanisms of catalysts degradation under 0.6-1.6 V versus RHE (Reversible Hydrogen Electrode) is still lacking. Herein, degradation mechanisms triggered by different defects on graphene supports are investigated by two cycling protocols. In the start-up/shutdown cycling (1.0-1.6 V vs. RHE), carbon oxidation reaction (COR) leads to shedding or swarm-like aggregation of Pt nanoparticles (NPs). Theoretical simulation results show that the expansion of vacancy defects promotes reaction kinetics of the decisive step in COR, reducing its reaction overpotential. While under the load cycling (0.6-1.0 V vs. RHE), oxygen containing defects lead to an elevated content of Pt in its oxidation state which intensifies Oswald ripening of Pt. The presence of vacancy defects can enhance the transfer of electrons from graphene to the Pt surface, reducing the d-band center of Pt and making it more difficult for the oxidation state of platinum to form in the cycling. This work will provide comprehensive understanding on Pt/Graphene catalysts degradation mechanisms.

Efficient ammonia synthesis from the air using tandem non-thermal plasma and electrocatalysis at ambient conditions

While electrochemical N2 reduction presents a sustainable approach to NH3 synthesis, addressing the emission- and energy-intensive limitations of the Haber-Bosch process, it grapples with challenges in N2 activation and competing with pronounced hydrogen evolution reaction. Here we present a tandem air-NOx-NOx--NH3 system that combines non-thermal plasma-enabled N2 oxidation with Ni(OH)x/Cu-catalyzed electrochemical NOx- reduction. It delivers a high NH3 yield rate of 3 mmol h-1 cm-2 and a corresponding Faradaic efficiency of 92% at -0.25 V versus reversible hydrogen electrode in batch experiments, outperforming previously reported ones. Furthermore, in a flow mode concurrently operating the non-thermal plasma and the NOx- electrolyzer, a stable NH3 yield rate of approximately 1.25 mmol h-1 cm-2 is sustained over 100 h using pure air as the intake. Mechanistic studies indicate that amorphous Ni(OH)x on Cu interacts with hydrated K+ in the double layer through noncovalent interactions and accelerates the activation of water, enriching adsorbed hydrogen species that can readily react with N-containing intermediates. In situ spectroscopies and density functional theory (DFT) results reveal that NOx- adsorption and their hydrogenation process are optimized over the Ni(OH)x/Cu surface. This work provides new insights into electricity-driven distributed NH3 production using natural air at ambient conditions.

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

Electrocatalytic nitrite reduction to ammonia on an Rh single-atom catalyst

Electrocatalytic NO2- reduction to NH3 (NO2RR) holds great promise as a green method for high-efficiency NH3 production. Herein, an Rh single-atom catalyst where isolated Rh supported on defective BN nanosheets (Rh1/BN) is reported to exhibit the exceptional NO2RR activity and selectivity. Extensive experimental and theoretical studies unveil that the high NO2RR performance of Rh1/BN arises from the single-atom Rh sites, which not only promote the activation and hydrogenation of NO2--to-NH3 process, but also hamper the undesired hydrogen evolution. Consequently, Rh1/BN assembled in a flow cell exhibits the highest NH3 yield rate of 2165.4 μmol h-1 cm-2 and FENH3 of 97.83 % at a high current density of 355.7 mA cm-2, ranking it the most efficient catalysts for NO2--to-NH3 conversion.

Enhanced Activity of Small Pt Nanoparticles Decorated with High-Loading Single Fe─N4 for Methanol Oxidation and Oxygen Reduction via the Assistive Active Sites Strategy

Decorating platinum (Pt) with a single atom offers a promising approach to tailoring their catalytic activity. In this study, for the first time, an innovative assistive active sites (AAS) strategy is proposed to construct high-loading (3.46wt.%) single Fe─N4 as AAS, which are further hybridized with small Pt nanoparticles to enhance both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) activities. For ORR, the target catalyst (Pt/HFeSA-HCS) exhibits a higher mass activity (MA) of 0.98 A mgPt -1 and specific activity (SA) of 1.39 mA cmPt -2 at 0.90 V versus RHE. As for MOR, Pt/HFeSA-HCS shows exceptional MA (3.21 A mgPt -1) and SA (4.27 mA cmPt -2) at peak values, surpassing commercial Pt/C by 15.3 and 11.5 times, respectively. The underlying mechanism behind this AAS strategy is to find that in MOR, Fe─N4 promotes water dissociation, generating more *OH to accelerate the conversion of *CO to CO2. Meanwhile, in ORR, Fe─N4 acts as a competitor to adsorb *OH, weakening Pt─OH bonding and facilitating desorption of *OH on the Pt surface. Constructing AAS that can enhance dual functionality simultaneously can be seen as a successful "kill two birds with one stone" strategy.

Concurrent Mechanisms of Hot Electrons and Interfacial Water Molecule Ordering in Plasmon-Enhanced Nitrogen Fixation

The participation of high-energy hot electrons generated from the non-radiative decay of localized surface plasmons is an important mechanism for promoting catalytic processes. Herein, another vital mechanism associated with the localized surface plasmon resonance (LSPR) effect, significantly contributing to the nitrogen reduction reaction (NRR), is found. That is to say, the LSPR-induced strong localized electric fields can weaken the intermolecular hydrogen bonds and regulate the arrangement of water molecules at the solid-liquid interface. The AuCu pentacle nanoparticles with excellent light absorption ability and the capability to generate strong localized electric fields are chosen to demonstrate this effect. The in situ Raman spectra and theoretical calculations are employed to verify the mechanism at the molecular scale in a nitrogen fixation process. Meanwhile, due to the promoted electron transfer at the interface by the well-ordered interfacial water, as well as the participation of high-energy hot electrons, the optimal catalyst exhibits excellent performance with an NH3 yield of 52.09 µg h-1 cm-2 and Faradaic efficiency (FE) of 45.82% at ─0.20 V versus RHE. The results are significant for understanding the LSPR effect in catalysis and provide a new approach for regulating the reaction process.

DFT Study of N-modified Co3Mo3C Electrocatalyst with Separated Active Sites for Enhanced Ammonia Oxidation

Since the facile oxidation of ammonia is one key for its utilization as a zero-carbon fuel in a direct ammonia fuel cell, developing the ammonia oxidation reaction (AOR) catalysts with cost-effective and higher activity is urgently required. However, the catalytic activity of AOR is limited by the scaling relationship of the intermediate adsorption. Based on the density functional theory, the N-modified Co3Mo3C with separated active sites of NH3 dehydrogenation and N-N coupling has been designed and investigated, which is a promising strategy to circumvent the scaling relationship, achieving improved AOR catalytic performance with a lower theoretical overpotential of 0.59 V under fast reaction kinetics condition. The calculation results show that the hollow site (Co-Mo-Mo and Co-Co-Mo) and Co site in N-modified Co3Mo3C play essential roles in NH3 dehydrogenation and N-N coupling, respectively. This work not only benefits for understanding the mechanism of AOR, but also provides a fundamental guidance for rational design of AOR catalysts.

Designing and Engineering Atomically Dispersed Metal Catalysts for CO2 to CO Conversion: From Single to Dual Metal Sites

The electrochemical CO2 reduction reaction (CO2 RR) is a promising approach to achieving sustainable electrical-to-chemical energy conversion and storage while decarbonizing the emission-heavy industry. The carbon-supported, nitrogen-coordinated, and atomically dispersed metal sites are effective catalysts for CO generation due to their high activity, selectivity, and earth abundance. Here, we discuss progress, challenges, and opportunities for designing and engineering atomic metal catalysts from single to dual metal sites. Engineering single metal sites using a nitrogen-doped carbon model was highlighted to exclusively study the effect of carbon particle sizes, metal contents, and M-N bond structures in the form of MN4 moieties on catalytic activity and selectivity. The structure-property correlation was analyzed by combining experimental results with theoretical calculations to uncover the CO2 to CO conversion mechanisms. Furthermore, dual-metal site catalysts, inheriting the merits of single-metal sites, have emerged as a new frontier due to their potentially enhanced catalytic properties. Designing optimal dual metal site catalysts could offer additional sites to alter the surface adsorption to CO2 and various intermediates, thus breaking the scaling relationship limitation and activity-stability trade-off. The CO2 RR electrolysis in flow reactors was discussed to provide insights into the electrolyzer design with improved CO2 utilization, reaction kinetics, and mass transport.

Electrocatalytic reduction of nitrite to ammonia on undercoordinated Cu

Electrocatalytic NO2--to-NH3 reduction (NO2RR) has emerged as an intriguing route for simultaneous mitigation of harmful nitrites and production of valuable NH3. Herein, we design for the first time undercoordinated Cu nanowires (u-Cu) as an efficient and selective NO2RR electrocatalyst, delivering the maximum NO2--to-NH3 faradaic efficiency of 94.7% and an ammonia production rate of 494.5 μmol h-1 cm-2 at -0.7 V vs. RHE. Theoretical calculations reveal that the created undercoordinated Cu sites on u-Cu can enhance NO2- adsorption, boost NO2--to-NH3 energetics and restrict competitive hydrogen evolution, thereby enabling the active and selective NO2RR.

Design Principles of Single-Atom Catalysts for Oxygen Evolution Reaction: From Targeted Structures to Active Sites

Hydrogen production from electrolytic water electrolysis is considered a viable method for hydrogen production with significant social value due to its clean and pollution-free nature, high hydrogen production efficiency, and purity, but the anode oxygen evolution reaction (OER) process is complex and kinetically slow. Single-atom catalysts (SACs) with 100% atom utilization and homogeneous active sites often exhibit high catalytic activity and are expected to be extensively applied. The catalytic performance of OER can be further improved by precise regulation of the structure through electronic effects, coordination environment, heteroatomic doping, and so on. In this review, the mechanisms of OER under different conditions are introduced, the latest research progress of SACs in the field of OER is systematically summarized, and then the effects of various structural regulation strategies on catalytic performance are discussed, and principles and ideas for the design of SACs for OER are proposed. In the end, the outstanding issues and current challenges in this field are summarized.

Activating doped graphene surface by cobalt-rich sulfide encapsulation toward oxygen reduction electrocatalysis

Similar to proton exchange membrane fuel cell, anion-exchange membrane fuel cell is also a significant energy conversion device for achieving the utilization of clean hydrogen energy. However, the cathodic alkaline oxygen reduction reaction (ORR) is kinetically not favored and usually requires platinum-group metal (PGM) catalysts such as Pt/C to reduce the overpotential. The major challenge in using PGM-free catalysts for ORR is their low efficiency and poor stability, which urgently demands new concepts and strategies to address this issue. Herein, we controllably manufactured a N, S-co doped graphene encapsulating uniform cobalt-rich sulfides (Co8FeS8@NSG) by a universal synthesis strategy. After encapsulation, electron transfer from the encapsulated cobalt-rich sulfides to the doped graphene was greatly promoted, which effectively optimizes the electronic structure of the doped graphene, thereby enhancing the ORR activity of the doped graphene surface. Consequently, the Co8FeS8@NSG exhibits enhanced ORR activity with a higher half-wave potential of 0.868 V (versus reversible hydrogen electrode, vs. RHE) when compared with pure NSG (0.765 V vs. RHE). Density functional theory calculations further confirm that the construction of interface for NSG encapsulating cobalt-rich sulfides could conspicuously elevate the ORR activity through slightly positively-charged C active site and thus simultaneously enhancing electronic conductivity.

Highly Selective Ammonia Oxidation on BiVO4 Photoanodes Co-catalyzed by Trace Amounts of Copper Ions

High-efficient photoelectrocatalytic direct ammonia oxidation reaction (AOR) conducted on semiconductor photoanodes remains a substantial challenge. Herein, we develop a strategy of simply introducing ppm levels of Cu ions (0.5-10 mg/L) into NH3 solutions to significantly improve the AOR photocurrent of bare BiVO4 photoanodes from 3.4 to 6.3 mA cm-2 at 1.23 VRHE , being close to the theoretical maximum photocurrent of BiVO4 (7.5 mA cm-2 ). The surface charge-separation efficiency has reached 90 % under a low bias of 0.8 VRHE . This AOR exhibits a high Faradaic efficiency (FE) of 93.8 % with the water oxidation reaction (WOR) being greatly suppressed. N2 is the main AOR product with FEs of 71.1 % in aqueous solutions and FEs of 100 % in non-aqueous solutions. Through mechanistic studies, we find that the formation of Cu-NH3 complexes possesses preferential adsorption on BiVO4 surfaces and efficiently competes with WOR. Meanwhile, the cooperation of BiVO4 surface effect and Cu-induced coordination effect activates N-H bonds and accelerates the first rate-limiting proton-coupled electron transfer for AOR. This simple strategy is further extended to other photoanodes and electrocatalysts.

The DFT and Machine Learning Method Accelerated the Discovery of DMSCs with High ORR and OER Catalytic Activities

The oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are crucial for the conversion of clean energy. Recently, dual-metal-site catalysts (DMSCs) have gained much attention due to their high atom utilization, stronger stability, and better catalytic performance. An advanced method that combines density functional theory (DFT) and machine learning (ML) has been employed in this study to investigate the adsorption free energies of adsorbates on hundreds of potential catalysts, with the aim of screening for catalysts that are highly active for the ORR and OER. The result of this study is that 30 DMSCs with ORR activity superior to Pt, 10 DMSCs with OER activity superior to RuO2, and 4 bifunctional catalysts for the OER and ORR are identified. This work provides guidance for the rational selection of metals on DMSCs to prepare catalysts with a high electrocatalytic performance for renewable energy applications.

Electronic Perturbation of Isolated Fe Coordination Structure for Enhanced Nitrogen Fixation

Modulation of the local electronic structure of isolated coordination structures plays a critical role in electrocatalysis yet remains a grand challenge. Herein, we have achieved electron perturbation for the isolated iron coordination structure via tuning the iron spin state from a high spin state (FeN4) to a medium state (FeN2B2). The transition of spin polarization facilitates electron penetration into the antibonding π orbitals of nitrogen and effectively activates nitrogen molecules, thereby achieving an ammonia yield of 115 μg h-1 mg-1cat. and a Faradaic efficiency of 24.8%. In situ spectroscopic studies and theoretical calculations indicate that boron coordinate sites, as electron acceptors, can regulate the adsorption energy of NxHy intermediates on the Fe center. FeN2B2 sites favor the NNH* intermediate formation and reduce the energy barrier of rate-determining steps, thus accounting for excellent nitrogen fixation performance. Our strategy provides an effective approach for designing efficient electrocatalysts via precise electronic perturbation.

Interface Engineering of PtZn Alloy and Nb2O5 for Promoting Ammonia Oxidation Reaction and Hydrogen Evolution Reaction

Ammonia electrolysis is a promising technology to obtain green hydrogen with zero-carbon emission, in which ammonia oxidation reaction (AOR) and hydrogen evolution reaction (HER) occur at the anode and cathode, respectively. However, the lack of efficient catalysts hinders its practical application. Herein, PtZn alloy is combined with Nb2O5 to construct a bifunctional heterostructure catalyst (PtZn-Nb2O5/C). The optimal sample with Nb2O5 content of 7.05 wt % demonstrates the best performance with a peak current density of 304.1 mA mg-1Pt for AOR, and it is only reduced by 17.0% after 4000 cycles of durability tests. For HER, it has a low overpotential of 34 mV at -10 mA cm-2 under the alkaline condition. This can be ascribed to the interfacial interaction between the PtZn alloy and Nb2O5, which adjusts the adsorption behavior of OHad to concurrently promote AOR and HER activity. This work thus proposes a viable strategy to design an efficient bifunctional catalyst for hydrogen generation from ammonia electrolysis.

Smart Aqueous Zinc Ion Battery: Operation Principles and Design Strategy

The zinc ion battery (ZIB) as a promising energy storage device has attracted great attention due to its high safety, low cost, high capacity, and the integrated smart functions. Herein, the working principles of smart responses, smart self-charging, smart electrochromic as well as smart integration of the battery are summarized. Thus, this review enables to inspire researchers to design the novel functional battery devices for extending their application prospects. In addition, the critical factors associated with the performance of the smart ZIBs are comprehensively collected and discussed from the viewpoint of the intellectualized design. A profound understanding for correlating the design philosophy in cathode materials and electrolytes with the electrode interface is provided. To address the current challenging issues and the development of smart ZIB systems, a wide variety of emerging strategies regarding the integrated battery system is finally prospected.

Ternary Heteroatomic Doping Induced Microenvironment Engineering of Low Fe-N4-Loaded Carbon Nanofibers for Bifunctional Oxygen Electrocatalysis

Fabricating highly efficient and long-life redox bifunctional electrocatalysts is vital for oxygen-related renewable energy devices. To boost the bifunctional catalytic activity of Fe-N-C single-atom catalysts, it is imperative to fine-tune the coordination microenvironment of the Fe sites to optimize the adsorption/desorption energies of intermediates during oxygen reduction/evolution reactions (ORR/OER) and simultaneously avoid the aggregation of atomically dispersed metal sites. Herein, a strategy is developed for fabricating a free-standing electrocatalyst with atomically dispersed Fe sites (≈0.89 wt.%) supported on N, F, and S ternary-doped hollow carbon nanofibers (FeN4 -NFS-CNF). Both experimental and theoretical findings suggest that the incorporation of ternary heteroatoms modifies the charge distribution of Fe active centers and enhances defect density, thereby optimizing the bifunctional catalytic activities. The efficient regulation isolated Fe centers come from the dual confinement of zeolitic imidazole framework-8 (ZIF-8) and polymerized ionic liquid (PIL), while the precise formation of distinct hierarchical three-dimensional porous structure maximizes the exposure of low-doping Fe active sites and enriched heteroatoms. FeN4 -NFS-CNF achieves remarkable electrocatalytic activity with a high ORR half-wave potential (0.90 V) and a low OER overpotential (270 mV) in alkaline electrolyte, revealing the benefit of optimizing the microenvironment of low-doping iron single atoms in directing bifunctional catalytic activity.

Fabrication of High Surface Area Fe/Fe3 O4 with Enhanced Performance for Electrocatalytic Nitrogen Reduction Reaction

The development of high-efficient and large-scale non-precious electrocatalysts to improve sluggish reaction kinetics plays a key role in enhancing electrocatalytic nitrogen reduction reaction (NRR) for ammonia production under mild condition. Herein, Fe3 O4 and Fe supported by porous carbon (denoted as Fe/Fe3 O4 /PC-800) composite with a high specific surface area of 1004.1 m2  g-1 was prepared via a simple template method. On one hand, the high surface area of Fe/Fe3 O4 /PC-800 provides a large area to enhance N2 adsorption and promote more protons and electrons to accelerate the reaction, thereby greatly improving the dynamics. On the other hand, mesoporous Fe/Fe3 O4 /PC-800 provides high electrochemically active surface area for promoting the occurrence of catalytic kinetics. As a result, Fe/Fe3 O4 /PC-800 exhibited significantly enhanced NRR performance with an ammonia yield of 31.15 μg h-1  mg-1 cat. and faraday efficiency of 22.26 % at -0.1 V vs. reversible hydrogen electrode (RHE). This study is expected to provide a new strategy for the synthesis of catalysts with large specific area and pave the way for the foundational research in NRR.

Ammonia Synthesis on Ternary LaSi-based Electrides: Tuning the Catalytic Mechanism by the Third Metal

Intermetallic electrides have recently drawn considerable attention due to their unique electronic structure and high catalytic performance for the activation of inert chemical bonds under mild conditions. However, the relationship between electride (anionic) electron abundance and catalytic performance is undefined; the key deciding factor for the performance of intermetallic electride catalysts remains to be addressed. Here, the secret behind electride catalysts La-TM-Si (TM=Co, Fe and Mn) with the same crystal structure but different anionic electrons was studied. Unexpectedly, LaCoSi with the least anionic electrons showed the best catalytic activity. The experiments and first-principles calculations showed that the electride anions promote the N2 dissociation which alters the rate-determining step (RDS) for ammonia synthesis on the studied electrides. Different reaction mechanisms were found for La-TM-Si (TM=Fe, Co) and LaMnSi. A dual-site module was revealed for LaCoSi and LaFeSi, in which transition metals were available for the N2 dissociation and La accelerates the NHx formation, respectively, breaking the Sabatier scaling relation. For LaMnSi, which is the most efficient for the N2 activation, the activity for ammonia synthesis is limited and confined by the scaling relations. The findings provide new insight into the working mechanism of intermetallic electrides.

Single-atom Cu anchored on Mo2C boosts nitrite electroreduction to ammonia

We design single-atom Cu anchored on Mo2C (Cu1/Mo2C) as an effective electrocatalyst towards electrochemical nitrite reduction to ammonia (NO2RR), exhibiting an NH3-faradaic efficiency of 91.5% with a corresponding NH3 yield rate of 472.9 μmol h-1 cm-2 at -0.6 V vs. RHE. Theoretical computations unravel that single-atomic Cu couples with the surface Mo atom of Mo2C to enable the construction of Cu-Mo dual-active centers, which can synergistically activate NO2- and minimize the NO2--to-NH3 reaction energy barrier, whilst suppressing the competing hydrogen evolution reaction.

N and S dual-coordinated Fe single-atoms in hierarchically porous hollow nanocarbon for efficient oxygen reduction

Fe-, and N-co-doped carbon (FeNC) electrocatalysts are promising alternatives to Pt-based catalysts for oxygen reduction reaction (ORR); however, simultaneously enhancing their intrinsic activity and exposure of Fe active sites remains challenging. Herein, we report S-modified Fe single-atom catalysts (SACs) anchored on N,S-co-doped hollow porous nanocarbon (Fe/NS-C) for ORR. The unique hollow structure and large surface area of the SACs are favorable for mass/electron transport and exposure of Fe single-atom active sites. The as-prepared Fe/NS-C electrocatalysts display a high-efficiency ORR activity with a half-wave potential of 0.893 V versus the reversible hydrogen electrode and exceed that of the benchmark commercial Pt/C catalyst as well as most reported transition-metal based SACs. Impressively, the Fe/NS-C-based Al-air battery (AAB) displays a high open circuit voltage of 1.48 V, a maximum power density of 140.16 mW cm-2, and satisfactory durability, outperforming commercial Pt/C-based AAB. Furthermore, Fe/NS-C exhibits considerable potential as a cathode catalyst for application in direct methanol fuel cells. Experimental and theoretical calculation results reveal that the excellent ORR performance of Fe/NS-C can be contributed to the highly active FeN3S sites and the unique hollow structure. This work provides new insights into the rational design and synthesis high-performance ORR electrocatalysts for energy conversion and storage devices. of employing ZIF-8 as precursors.

Ampere-Level Nitrate Electroreduction to Ammonia over Monodispersed Bi-Doped FeS2

Electrochemical conversion of NO3- into NH3 (NO3RR) holds an enormous prospect to simultaneously yield valuable NH3 and alleviate NO3- pollution. Herein, we report monodispersed Bi-doped FeS2 (Bi-FeS2) as a highly effective NO3RR catalyst. Atomic coordination characterizations of Bi-FeS2 disclose that the isolated Bi dopant coordinates with its adjacent Fe atom to create the unconventional p-d hybridized Bi-Fe dinuclear sites. Operando spectroscopic measurements combined with theoretical calculations disclose that Bi-Fe dinuclear sites can synergistically enhance the hydrogenation energetics of NO3--to-NH3 pathway, while suppressing the competitive hydrogen evolution, leading to a high NO3RR selectivity and activity. Consequently, the specially designed flow cell equipped with Bi-FeS2 exhibits a high NH3 yield rate of 83.7 mg h-1 cm-2 with a near-100% NO3--to-NH3 Faradaic efficiency at an ampere-level current density of 1023.2 mA cm-2, together with an excellent long-term stability for 100 h of electrolysis, ranking almost the highest performance among all reported NO3RR catalysts.

Electrocatalytic Water Oxidation Activity-Stability Maps for Perovskite Oxides Containing 3d, 4d and 5d Transition Metals

Improving catalytic activity without loss of catalytic stability is one of the core goals in search of low-iridium-content oxygen evolution electrocatalysts under acidic conditions. Here, we synthesize a family of 66 SrBO3 perovskite oxides (B=Ti, Ru, Ir) with different Ti : Ru : Ir atomic ratios and construct catalytic activity-stability maps over composition variation. The maps classify the multicomponent perovskites into chemical groups with distinct catalytic activity and stability for acidic oxygen evolution reaction, and highlights a chemical region where high catalytic activity and stability are achieved simultaneously at a relatively low iridium level. By quantifying the extent of hybridization of mixed transition metal 3d-4d-5d and oxygen 2p orbitals for multicomponent perovskites, we demonstrate this complex interplay between 3d-4d-5d metals and oxygen atoms in governing the trends in both activity and stability as well as in determining the catalytic mechanism involving lattice oxygen or not.

A Conceptual Approach for the Design of New Catalysts for Ammonia Synthesis: A Metal-Support Interactions Review

The growing interest in green ammonia production has spurred the development of new catalysts with the potential to carry out the Haber-Bosch process under mild pressure and temperature conditions. While there is a wide experimental background on new catalysts involving transition metals, supports and additives, the fundamentals behind ammonia synthesis performance on these catalysts remained partially unsolved. Here, we review the most important works developed to date and analyze the traditional catalysts for ammonia synthesis, as well as the influence of the electron transfer properties of the so-called 3rd-generation catalysts. Finally, the importance of metal-support interactions is highlighted as an effective pathway for the design of new materials with potential to carry out ammonia synthesis at low temperatures and pressures.

Efficient and complete dehydrogenation of hydrazine borane over a CoPt catalyst

Bimetallic CoPt alloy nanoparticles (NPs) immobilized on CeO2 nanorods (CoPt/CeO2) were synthesized by a facile wet-chemistry reduction method, which showed the highest catalytic efficiency reported to date for the complete dehydrogenation of hydrazine borane with a high TOF value of up to 5454 h-1 at 323 K.

Self-Construction of Efficient Interfaces Ensures High-Performance Direct Ammonia Protonic Ceramic Fuel Cells

Direct ammonia protonic ceramic fuel cells (PCFCs) are highly efficient energy conversion devices since ammonia as a carbon-neutral hydrogen-rich carrier shows great potential for storage and long-distance transportation when compared with hydrogen fuel. However, traditional Ni-based anodes readily suffer from severe structural destruction and dramatic deactivation after long-time exposure to ammonia. Here a Sr2 Fe1.35 Mo0.45 Cu0.2 O6-δ (SFMC) anode catalytic layer (ACL) painted onto a Ni-BaZr0.1 Ce0.7 Y0.1 Yb0.1 O3- δ (BZCYYb) anode with enhanced catalytic activity and durability toward the direct utilization of ammonia is reported. A tubular Ni-BZCYYb anode-supported cells with the SFMC ACL show excellent peak power densities of 1.77 W cm-2 in wet H2 (3% H2 O) and 1.02 W cm-2 in NH3 at 650 °C. A relatively stable operation of the cells is obtained at 650 °C for 200 h in ammonia fuel. Such achieved improvements in the activity and durability are attributed to the self-constructed interfaces with the phases of NiCu or/and NiFe for efficient NH3 decomposition, resulting in a strong NH3 adsorption strength of the SFMC, as confirmed by NH3 thermal conversion and NH3 -temperature programmed desorption. This research offers a valuable strategy of applying an internal catalytic layer for highly active and durable ammonia PCFCs.

Nanoengineering Metal-Organic Frameworks and Derivatives for Electrosynthesis of Ammonia

Electrocatalytic synthesis under mild conditions has become increasingly important as one of the practical alternatives for industrial applications, especially for the green ammonia (NH3) industry. A properly engineered electrocatalyst plays a vital role in the realization of superior catalytic performance. Among various types of promising nanomaterials, metal-organic frameworks (MOFs) are competitive candidates for developing efficient electrocatalytic NH3 synthesis from simple nitrogen-containing molecules or ions, such as N2 and NO3-. In this review, recent advances in the development of electrocatalysts derived from MOFs for the electrosynthesis of NH3 are collected, categorized, and discussed, including their application in the N2 reduction reaction (NRR) and the NO3- reduction reaction (NO3RR). Firstly, the fundamental principles are illustrated, such as plausible mechanisms of NH3 generation from N2 and NO3-, the apparatus of corresponding electrocatalysis, parameters for evaluation of reaction efficiency, and detection methods of yielding NH3. Then, the electrocatalysts for NRR processes are discussed in detail, including pristine MOFs, MOF-hybrids, MOF-derived N-doped porous carbons, single atomic catalysts from pyrolysis of MOFs, and other MOF-related materials. Subsequently, MOF-related NO3RR processes are also listed and discussed. Finally, the existing challenges and prospects for the rational design and fabrication of electrocatalysts from MOFs for electrochemical NH3 synthesis are presented, such as the evolution of investigation methods with artificial intelligence, innovation in synthetic methods of MOF-related catalysts, advancement of characterization techniques, and extended electrocatalytic reactions.

Ruthenium-Manganese Solid Solution Oxide with Enhanced Performance for Acidic and Alkaline Oxygen Evolution Reaction

Proton exchange membrane water electrolysers and alkaline exchange membrane water electrolysers for hydrogen production suffer from sluggish kinetics and the limited durability of the electrocatalyst toward oxygen evolution reaction (OER). Herein, a rutile Ru0.75 Mn0.25 O2-δ solid solution oxide featured with a hierarchical porous structure has been developed as an efficient OER electrocatalyst in both acidic and alkaline electrolyte. Specifically, compared with commercial RuO2 , the catalyst displays a superior reaction kinetics with small Tafel slope of 54.6 mV dec-1 in 0.5 M H2 SO4 , thus allowing a low overpotential of 237 and 327 mV to achieve the current density of 10 and 100 mA cm-2 , respectively, which is attributed to the enhanced electrochemically active surface area from the porous structure and the increased intrinsic activity owing to the regulated Ru>4+ proportion with Mn incorporation. Additionally, the sacrificial dissolution of Mn relieves the leaching of active Ru species, leading to the extended OER durability. Besides, the Ru0.75 Mn0.25 O2-δ catalyst also shows a highly improved OER performance in alkaline electrolyte, rendering it a versatile catalyst for water splitting.

Atomically Dispersed Ni-N4 Sites Assist Pt3 Ni Nanocages with Pt Skin to Synergistically Enhance Oxygen Reduction Activity and Stability

Currently, the rarity and high cost of platinum (Pt)-based electrocatalysts seriously limit their commercial application in fuel cells cathode. Decorating Pt with atomically dispersed metal-nitrogen sites possibly offers an effective pathway to synergy tailor their catalytic activity and stability. Here active and stable oxygen reduction reaction (ORR) electrocatalysts (Pt₃ Ni@Ni-N₄ -C) by in situ loading Pt₃ Ni nanocages with Pt skin on single-atom nickel-nitrogen (Ni-N₄ ) embedded carbon supports are designed and constructed. The Pt₃ Ni@Ni-N₄ -C exhibits excellent mass activity (MA) of 1.92 A mg_Pt ^-1 and specific activity of 2.65 mA cm_Pt ^-2 , together with superior durability of 10 mV decay in half-wave potential and only 2.1% loss in MA after 30 000 cycles. Theoretical calculations demonstrate that Ni-N₄ sites significant redistribute of electrons and make them transfer from both the adjacent carbon and Pt atoms to the Ni-N₄ . The resultant electron accumulation region successfully anchored Pt₃ Ni, that not only improves structural stability of the Pt₃ Ni, but importantly makes the surface Pt more positive to weaken the adsorption of *OH to enhance ORR activity. This strategy lays the groundwork for the development of super effective and durable Pt-based ORR catalysts.

In Situ Filling of the Oxygen Vacancies with Dual Heteroatoms in Co3O4 for Efficient Overall Water Splitting

Electrocatalytic water splitting is a crucial area in sustainable energy development, and the development of highly efficient bifunctional catalysts that exhibit activity toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of paramount importance. Co₃O₄ is a promising candidate catalyst, owing to the variable valence of Co, which can be exploited to enhance the bifunctional catalytic activity of HER and OER through rational adjustments of the electronic structure of Co atoms. In this study, we employed a plasma-etching strategy in combination with an in situ filling of heteroatoms to etch the surface of Co₃O₄, creating abundant oxygen vacancies, while simultaneously filling them with nitrogen and sulfur heteroatoms. The resulting N/S-V_O-Co₃O₄ exhibited favorable bifunctional activity for alkaline electrocatalytic water splitting, with significantly enhanced HER and OER catalytic activity compared to pristine Co₃O₄. In an alkaline overall water-splitting simulated electrolytic cell, N/S-V_O-Co₃O₄ || N/S-V_O-Co₃O₄ showed excellent overall water splitting catalytic activity, comparable to noble metal benchmark catalysts Pt/C || IrO₂, and demonstrated superior long-term catalytic stability. Additionally, the combination of in situ Raman spectroscopy with other ex situ characterizations provided further insight into the reasons behind the enhanced catalyst performance achieved through the in situ incorporation of N and S heteroatoms. This study presents a facile strategy for fabricating highly efficient cobalt-based spinel electrocatalysts incorporated with double heteroatoms for alkaline electrocatalytic monolithic water splitting.

A metal-free catalyst for electrocatalytic NO reduction to NH3

Metal-free boron phosphide (BP) is explored for the first time as an effective catalyst for electrocatalytic NO reduction to NH₃, showing a high NH₃-faradaic efficiency of 83.3% with an NH₃ yield rate of 96.6 μmol h^-1 cm^-2, surpassing most metal-based catalysts. Theoretical results reveal that the B and P atoms of BP can serve as dual-active centers to synergistically activate NO, promote the NORR hydrogenation process and inhibit the competing hydrogen evolution reaction.

Dispersing small Ru nanoparticles into boron nitride remodified by reduced graphene oxide for high-efficient electrocatalytic hydrogen evolution reaction

Ruthenium (Ru) electrocatalysts suffer from excessive aggregation during the hydrogen evolution reaction (HER), which hinders their practical application for hydrogen production. Hexagonal boron nitride (h-BN) is a potential carrier that could solve the above problem, but its wide band gap and low conductivity become obstacles. Herein, we provide a new, facile, low-cost, and effective strategy (killing two birds with one stone) to overcome the above issues. After modifying h-BN with reduced graphene oxide (rGO), a small amount of Ru nanoparticles (NPs) (2.2 %) are dispersed into BN with approximately uniform distribution and size control of Ru nanoparticles (∼3.85 nm). The strong synergy between Ru NPs and BN@C in the optimal Ru/BN@C (Ru wt.% = 2.22 %) electrocatalyst endows it an outstanding HER activity, with small HER overpotentials (η₁₀ = 32 mV, 35 mV) and low Tafel slopes (33.89 mV dec^-1, 37.66 mV dec^-1) in both 1 M KOH and 0.5 M H₂SO₄ media, respectively, along with good long-term stability for 50 h. Based on density functional theory (DFT) calculations, the addition of Ru to BN has been successful in creating fresh active sites for H*, with good possible adsorption/desorption ability (ΔG_H* = -0.24 eV) while preserving low water dissociation (ΔG_b = 0.46 eV) in an alkaline environment. As a result, the Ru/BN composite exhibits outstanding HER activity in both acidic and alkaline conditions. Furthermore, this study provides, for the first time, a template-free strategy to develop a good and low-cost supporter (BN) for dispersing other noble metals and the formation of highly efficient HER/OER electrocatalysts.

P-Block Metal-Based Electrocatalysts for Nitrogen Reduction to Ammonia: A Minireview

Electrochemical nitrogen reduction reaction (NRR) to ammonia (NH₃ ) using renewable electricity provides a promising approach towards carbon neutral. What's more, it has been regarded as the most promising alternative to the traditional Haber-Bosch route in current context of developing sustainable technologies. The development of a class of highly efficient electrocatalysts with high selectivity and stability is the key to electrochemical NRR. Among them, P-block metal-based electrocatalysts have significant application potential in NRR for which possessing a strong interaction with the N 2p orbitals. Thus, it offers a good selectivity for NRR to NH₃ . The density of state (DOS) near the Fermi level is concentrated for the P-block metal-based catalysts, indicating the ability of P-block metal as active sites for N₂ adsorption and activation by donating p electrons. In this work, we systematically review the recent progress of P-block metal-based electrocatalysts for electrochemical NRR. The effect of P-block metal-based electrocatalysts on the NRR activity, selectivity and stability are discussed. Specifically, the catalyst design, the nature of the active sites of electrocatalysts and some strategies for boosting NRR performance, the reaction mechanism, and the impact of operating conditions are unveiled. Finally, some challenges and outlooks using P-block metal-based electrocatalysts are proposed.

The material-microorganism interface in microbial hybrid electrocatalysis systems

This review presents a comprehensive summary of the material-microorganism interface in microbial hybrid electrocatalysis systems. Microbial hybrid electrocatalysis has been developed to combine the advantages of inorganic electrocatalysis and microbial catalysis. However, electron transfer at the interfaces between microorganisms and materials is a very critical issue that affects the efficiency of the system. Therefore, this review focuses on the electron transfer at the material-microorganism interface and the strategies for building efficient microorganism and material interfaces. We begin with a brief introduction of the electron transfer mechanism in both the bioanode and biocathode of bioelectrochemical systems to understand the material-microorganism interface. Next, we summarise the strategies for constructing efficient material-microorganism interfaces including material design and modification and bacterial engineering. We also discuss emerging studies on the bio-inorganic hybrid electrocatalysis system. Understanding the interface between electrode/active materials and the microorganisms, especially the electron transfer processes, could help to drive the evolution of material-microorganism hybrid electrocatalysis systems towards maturity.

Oxygen Evolution/Reduction Reaction Catalysts: From In Situ Monitoring and Reaction Mechanisms to Rational Design

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core steps of various energy conversion and storage systems. However, their sluggish reaction kinetics, i.e., the demanding multielectron transfer processes, still render OER/ORR catalysts less efficient for practical applications. Moreover, the complexity of the catalyst-electrolyte interface makes a comprehensive understanding of the intrinsic OER/ORR mechanisms challenging. Fortunately, recent advances of in situ/operando characterization techniques have facilitated the kinetic monitoring of catalysts under reaction conditions. Here we provide selected highlights of recent in situ/operando mechanistic studies of OER/ORR catalysts with the main emphasis placed on heterogeneous systems (primarily discussing first-row transition metals which operate under basic conditions), followed by a brief outlook on molecular catalysts. Key sections in this review are focused on determination of the true active species, identification of the active sites, and monitoring of the reactive intermediates. For in-depth insights into the above factors, a short overview of the metrics for accurate characterizations of OER/ORR catalysts is provided. A combination of the obtained time-resolved reaction information and reliable activity data will then guide the rational design of new catalysts. Strategies such as optimizing the restructuring process as well as overcoming the adsorption-energy scaling relations will be discussed. Finally, pending current challenges and prospects toward the understanding and development of efficient heterogeneous catalysts and selected homogeneous catalysts are presented.

Tandem Electrocatalytic Nitrate Reduction to Ammonia on MBenes

We demonstrate the great feasibility of MBenes as a new class of tandem catalysts for electrocatalytic nitrate reduction to ammonia (NO₃ RR). As a proof of concept, FeB₂ is first employed as a model MBene catalyst for the NO₃ RR, showing a maximum NH₃ -Faradaic efficiency of 96.8 % with a corresponding NH₃ yield of 25.5 mg h^-1  cm^-2 at -0.6 V vs. RHE. Mechanistic studies reveal that the exceptional NO₃ RR activity of FeB₂ arises from the tandem catalysis mechanism, that is, B sites activate NO₃ ^- to form intermediates, while Fe sites dissociate H₂ O and increase *H supply on B sites to promote the intermediate hydrogenation and enhance the NO₃ ^- -to-NH₃ conversion.

Highly efficient metal-free borocarbonitride catalysts for electrochemical reduction of N2 to NH3

The electrocatalytic nitrogen reduction reaction (NRR) for ammonia (NH₃) under ambient conditions is emerging as a potentially sustainable alternative to the traditional, energy-intensive Haber-Bosch process for ammonia production. Currently, metal-based electrocatalysts constitute the majority of reported NRR catalysts. However, they often suffer from the shortcomings of competitive reactions of nitrogen adsorption/activation and hydrogen generation. Therefore, there is an urgent need to develop more environmentally friendly, low energy consumption, and non-polluting high-performance metal-free electrocatalysts. In this study, borocarbonitride (BCN) materials derived from boron imidazolate framework (BIF-20) were used to boost efficient electrochemical nitrogen conversion to ammonia under ambient conditions. The BCN catalyst demonstrated excellent performance in 0.1 M KOH, with an ammonia yield of 21.62 μg h^-1 mg_cat^-1 and a Faradaic efficiency of 9.88% at -0.3 V (Reversible Hydrogen Electrode, RHE). This performance is superior to most metal-free catalysts and even some metal catalysts for NRR. The ¹⁵N₂/¹⁴N₂ isotope labeling experiments and density functional theory (DFT) calculations showed that N₂ can be adsorbed and converted to NH₃ on the surface of BCN, and that the energy barrier can be significantly reduced by structural design for BCN. This work highlights the important role played by the presence of Lewis acid-base pairs in metal-free catalysts for enhancing electrochemical NRR performance.

Biowaste-Derived Heteroatom-Doped Porous Carbon as a Sustainable Electrocatalyst for Hydrogen Evolution Reaction

Heteroatom-doped porous carbon material (H-PCM) was synthesized using Anacardium occidentale (cashew) nut’s skin by a simple pyrolysis route. The resulting H-PCM was thoroughly characterized by various analytical techniques such as field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray (EDX) spectroscopy, high-resolution transmittance electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, nitrogen adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The obtained results strongly demonstrated that the synthesized H-PCM exhibited a porous nature, continuous sponge-like and sheet-like smooth morphology, and a moderate degree of graphitization/crystallinity with oxygen-, nitrogen-, and sulfur-containing functionalities in the carbon matrix. After the structural confirmation, as-prepared H-PCM has used a sustainable electrocatalyst for hydrogen evolution reaction (HER) because the metal-free carbonaceous catalysts are one of the most promising candidates. The H-PCM showed excellent HER activities with a lowest Tafel slope of 75 mV dec−1 and durable stability in 0.5 M H2SO4 aqueous solution. Moreover, this work provides a versatile and effective strategy for designing excellent metal-free electrocatalysts from the cheapest biowaste/biomass for large-scale production of hydrogen gas through electrochemical water splitting.

Tailored Bimetallic Ni-Sn Catalyst for Electrochemical Ammonia Oxidation to Dinitrogen with High Selectivity

Direct electrochemical ammonia oxidation reaction (eAOR) is an efficient and sustainable strategy to process wastewater containing ammonia, and it endures overoxidation and severely competitive oxygen evolution reaction (OER). Herein, we synthesized a Ni(OH)₂/SnO₂ composite catalyst by a multistep strategy and applied it to the eAOR process. Ni(OH)₂/SnO₂ exhibited a N₂-N Faradaic efficiency (FE_N2-N) of 84.2%, with a N₂ partial current density (j_N2-N) of 2.7 mA cm^-2 at 1.55 V vs reversible hydrogen electrode (RHE) in 0.5 M K₂SO₄ with 10 mM NH₃-N (pH 11). The oxophilic Sn promoted NH₃ absorption on Ni sites while suppressing the OER. As the active species, NiOOH accelerated the dimerization of intermediates (*NH₂ or *NH) to form N₂.

Achievements, Challenges, and Perspectives on Nitrogen Electrochemistry for Carbon-Neutral Energy Technologies

Unrestrained anthropogenic activities have severely disrupted the global natural nitrogen cycle, causing numerous energy and environmental issues. Electrocatalytic nitrogen transformation is a feasible and promising strategy for achieving a sustainable nitrogen economy. Synergistically combining multiple nitrogen reactions can realize efficient renewable energy storage and conversion, restore the global nitrogen balance, and remediate environmental crises. Here, we provide a unique aspect to discuss the intriguing nitrogen electrochemistry by linking three essential nitrogen-containing compounds (i.e., N₂ , NH₃ , and NO₃ ^- ) and integrating four essential electrochemical reactions, i.e., the nitrogen reduction reaction (N₂ RR), nitrogen oxidation reaction (N₂ OR), nitrate reduction reaction (NO₃ RR), and ammonia oxidation reaction (NH₃ OR). This minireview also summarizes the acquired knowledge of rational catalyst design and underlying reaction mechanisms for these interlinked nitrogen reactions. We further underscore the associated clean energy technologies and a sustainable nitrogen-based economy.

Corrosion Chemistry of Electrocatalysts

Electrocatalysts are the core components of many sustainable energy conversion technologies that are considered the most potential solution to the worldwide energy and environmental crises. The reliability of structure and composition pledges that electrocatalysts can achieve predictable and stable performance. However, during the electrochemical reaction, electrocatalysts are influenced directly by the applied potential, the electrolyte, and the adsorption/desorption of reactive species, triggering structural and compositional corrosion, which directly affects the catalytic behaviors of electrocatalysts (performance degradation or enhancement) and invalidates the established structure-activity relationship. Therefore, it is necessary to elucidate the corrosion behavior and mechanism of electrocatalysts to formulate targeted corrosion-resistant strategies or use corrosion reconstruction synthesis techniques to guide the preparation of efficient and stable electrocatalysts. Herein, the most recent developments in electrocatalyst corrosion chemistry are outlined, including corrosion mechanisms, mitigation strategies, and corrosion syntheses/reconstructions based on typical materials and important electrocatalytic reactions. Finally, potential opportunities and challenges are also proposed to foresee the possible development in this field. It is believed that this contribution will raise more awareness regarding nanomaterial corrosion chemistry in energy technologies and beyond.