Anode catalysts for direct methanol fuel cells in acidic media: do we have any alternative for Pt or Pt-Ru?

Pt3Sn0.5Mn0.5 Intermetallic Electrocatalyst with Superior Stability for CO-Resilient Methanol Oxidation

The sluggish kinetics of methanol oxidation reaction (MOR) and poor long-term durability of catalysts are the main restrictions of the large-scale applications of direct methanol fuel cells (DMFCs). Herein, we demonstrated an inspirational ternary Pt3Sn0.5Mn0.5/DMC intermetallic catalyst that reached 4.78 mA cm-2 and 2.39 A mg-1Pt for methanol oxidation, which were 2.50/2.44 and 5.62/5.31 times that of commercial PtRu/C and Pt/C. After the durability test, Pt3Sn0.5Mn0.5/DMC presented a very low current density attenuation (38.5%), which was significantly lower than those for commercial PtRu/C catalyst (84.2%) and Pt/C (93.1%). Density functional theory (DFT) calculations revealed that the coregulation of Sn and Mn altered the surface electronic structure and endowed Pt3Sn0.5Mn0.5 with selective adsorption of Pt for CO and Sn for OH, which optimized the adsorption strength for intermediates and improved the reaction kinetics of MOR. Beyond offering an advanced electrocatalyst, this study provided a new point of view for the rational design of superior methanol oxidation catalysts for DMFC.

Probing the adsorption configuration of methanol at a charged air/aqueous interface using nonlinear spectroscopy

Investigating the effects of electrolyte ions on the adsorption configuration of methanol at a charged interface is important for studying the interface structure of electrolyte solutions and the oxidation mechanism of methanol in fuel cells. This study uses sum frequency generation (SFG) and heterodyne-detected second harmonic generation (HD-SHG) to investigate the adsorption configuration of methanol at the air/aqueous interface of 0.1 M NaClO4 solution, 0.1 M HClO4 solution and pure water. The results elucidate that the ion effect in the electrolyte solution affects the interface's charged state and the methanol's adsorption conformation at the interface. The negatively charged surface of the 0.1 M NaClO4 solution and the positively charged surface of the 0.1 M HClO4 solution arise from the corresponding specific ionic effects of the electrolyte solution. The orientation angle of methyl with respect to the surface normal is 43.4° ± 0.1° at the 0.1 M NaClO4 solution surface and 21.5° ± 0.2° at the 0.1 M HClO4 solution surface. Examining these adsorption configurations in detail, we find that at the negatively charged surface the inclined orientation angle (43.4°) of methanol favors the hydroxymethyl production by breaking the C-H bond, while at the positively charged surface the upright orientation angle (21.5°) of methanol promotes the methoxy formation by breaking the O-H bond. These findings not only illuminate the intricate ion effects on small organic molecules but also contribute to a molecular-level comprehension of the oxidation mechanism of methanol at electrode interfaces.

Surface-Enriched Single-Bi-Atoms Tailoring of Pt Nanorings for Direct Methanol Fuel Cells with Ultralow-Pt-Loading

Single-atom decorating of Pt emerges as a highly effective strategy to boost catalytic properties, which can trigger the most Pt active sites while blocking the smallest number of Pt atoms. However, the rational design and creation of high-density single-atoms on Pt surface remain as a huge challenge. Herein, a customized synthesis of surface-enriched single-Bi-atoms tailored Pt nanorings (SE-Bi1/Pt NRs) toward methanol oxidation is reported, which is guided by the density functional theory (DFT) calculations suggesting that a relatively higher density of Bi species on Pt surface can ensure a CO-free pathway and accelerate the kinetics of *HCOOH formation. Decorating Pt NRs with dense single-Bi-atoms is achieved by starting from PtBi intermetallic nanoplates (NPs) with intrinsically isolated Bi atoms and subsequent etching and annealing treatments. The SE-Bi1/Pt NRs exhibit a mass activity of 23.77 A mg-1 Pt toward methanol oxidation in alkaline electrolyte, which is 2.2 and 12.8 times higher than those of Pt-Bi NRs and Pt/C, respectively. This excellent activity endows the SE-Bi1/Pt NRs with a high likelihood to be used as a practical anodic electrocatalyst for direct methanol fuel cells （DMFCs） with high power density of 85.3 mW cm-2 and ultralow Pt loading of 0.39 mg cm-2.

Lutetium-Induced Ultrafine PtRu Nanoclusters with a High Electrochemical Surface Area for Direct Methanol Fuel Cells at Alleviated Temperatures

PtRu alloys have been recognized as the state-of-the-art catalysts for the methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs). However, their applications in DMFCs are still less efficient in terms of both catalytic activity and durability. Rare earth (RE) metals have been recognized as attractive elements to tune the catalytic activity, while it is still a world-class challenge to synthesize well-dispersed Pt-RE alloys. Herein, we developed a novel hydrogen-assisted magnesiothermic reduction strategy to prepare a highly dispersed carbon-supported lutetium-doped PtRu catalyst with ultrafine nanoclusters and atomically dispersed Ru sites. The PtRuLu catalyst shows an outstanding high electrochemical surface area (ECSA) of 239.0 m2 gPt-1 and delivers an optimized MOR mass activity and specific activity of 632.5 mA mgPt-1 and 26 A cmPt-2 at 0.4 V vs saturated calomel electrode (SCE), which are 3.6 and 3.5 times of commercial PtRu-JM and an order higher than PtLu, respectively. These novel catalysts have been demonstrated in a high-temperature direct methanol fuel cell running in a temperature range of 180-240 °C, achieving a maximum power density of 314.3 mW cm-2. The AC-STEM imaging, in situ ATR-IR spectroscopy, and DFT calculations disclose that the high performance is resulted from the highly dispersed PtRuLu nanoclusters and the synergistic effect of the atomically dispersed Ru sites with PtRuLu nanoclusters, which significantly reduces the CO* intermediates coverage due to the promoted water activation to form the OH* to facilitate the CO* removal.

Amorphization Activated Multimetallic Pd Alloys for Boosting Oxygen Reduction Catalysis

Amorphous nanomaterials have drawn extensive attention owing to their unique features, while amorphization on noble metal nanomaterials still remains formidably challenging. Herein, we demonstrate a universal strategy to synthesize amorphous Pd-based nanomaterials from unary to quinary metals through the introduction of phosphorus (P). The amorphous Pd-based nanoparticles (NPs) exhibit generally promoted oxygen reduction reaction (ORR) activity and durability compared with their crystalline counterparts. Significantly, the quinary P-PdCuNiInSn NPs, benefiting from the amorphous structure and multimetallic component effect, exhibit mass activities as high as 1.04 A mgPd-1 and negligible activity decays of 1.8% among the stability tests, which are much better than values for original Pd NPs (0.134 A mgPd-1 and 28.4%). Experimental and theoretical analyses collectively reveal that the synergy of P-induced amorphization and the expansion of metallic components can considerably lower the free energy changes in the rate-determined step, thereby explaining the positive correlation with the catalytic activity.

Tailoring the Activity of Electrocatalytic Methanol Oxidation on Cobalt Hydroxide by the Incorporation of Catalytically Inactive Zinc Ions

Catalytically inactive Zn2+ is incorporated into cobalt hydroxide to synthesize hierarchical ZnCo-layered double hydroxide nanosheet networks supported on carbon fiber (ZnCo-LDH/CF). The incorporation of Zn2+ is revealed to endow ZnCo-LDH/CF with significantly superior performance in the aspects of the activity and selectivity for methanol electrooxidation to formic acid and the boosting effect for cathodic hydrogen production compared with the counterpart without Zn2+. Density functional theory (DFT) calculation reveals that the incorporation of nonactive Zn2+ can increase the density of states near the Fermi level of LDH (i.e., elevate electrical conductivity to form favorable charge transportation during electrocatalysis) and promote the adsorption and subsequent cleavage of methanol, thus leading to the enhanced methanol electrooxidation performance.

Review: chitosan-based biopolymers for anion-exchange membrane fuel cell application

Chitosan (CS)-based anion exchange membranes (AEMs) have gained significant attention in fuel cell applications owing to their numerous benefits, such as environmental friendliness, flexibility for structural alteration, and improved mechanical, thermal and chemical durability. This study aims to enhance the cell performance of CS-based AEMs by addressing key factors including mechanical stability, ionic conductivity, water absorption and expansion rate. While previous reviews have predominantly focused on CS as a proton-conducting membrane, the present mini-review highlights the advancements of CS-based AEMs. Furthermore, the study investigates the stability of cationic head groups grafted to CS through simulations. Understanding the chemical properties of CS, including the behaviour of grafted head groups, provides valuable insights into the membrane's overall stability and performance. Additionally, the study mentions the potential of modern cellulose membranes for alkaline environments as promising biopolymers. While the primary focus is on CS-based AEMs, the inclusion of cellulose membranes underscores the broader exploration of biopolymer materials for fuel cell applications.

Combining Renewable Electricity and Renewable Carbon: Understanding Reaction Mechanisms of Biomass-Derived Furanic Compounds for Design of Catalytic Nanomaterials

ConspectusDespite the growing deployment of renewable energy conversion technologies, a number of large industrial sectors remain challenging to decarbonize. Aviation, heavy transport, and the production of steel, cement, and chemicals are heavily dependent on carbon-containing fuels and feedstocks. A hopeful avenue toward carbon neutrality is the implementation of renewable carbon for the synthesis of critical fuels, chemicals, and materials. Biomass provides an opportune source of renewable carbon, naturally capturing atmospheric CO2 and forming multicarbon linkages and useful chemical functional groups. The constituent molecules nonetheless require various chemical transformations, often best facilitated by catalytic nanomaterials, in order to access usable final products.Catalyzed transformations of renewable biomass compounds may intersect with renewable energy production by offering a means to utilize excess intermittent electricity and store it within chemical bonds. Electrochemical catalytic processes can often offer advantages in energy efficiency, product selectivity, and modular scalability compared to thermal-driven reactions. Electrocatalytic reactions with renewable carbon feedstocks can further enable related processes such as water splitting, where value-adding organic oxidation reactions may replace the evolution of oxygen. Organic electroreduction reactions may also allow desirable hydrogenations of bonds without intermediate formation of H2 and need for additional reactors.This Account highlights recent work aimed at gaining a fundamental understanding of transformations involving biomass-derived molecules in electrocatalytic nanomaterials. Particular emphasis is placed on the oxidation of biomass derived furanic compounds such as furfural and 5-hydroxymethylfurfural (HMF), which can yield value-added chemicals, including furoic acid (FA), maleic acid (MA), and 2,5-furandicarboxylic acid (FDCA) for renewable materials and other commodities. We highlight advanced implementations of online electrochemical mass spectrometry (OLEMS) and vibrational spectroscopies such as attenuated total reflectance surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS), combined with microkinetic models (MKMs) and quantum chemical calculations, to shed light on the elementary mechanistic pathways involved in electrochemical biomass conversion and how these paths are influenced by catalytic nanomaterials. Perspectives are given on the potential opportunities for materials development toward more efficient and selective carbon-mitigating reaction pathways.

Layer-by-Layer Assembly of CTAB-rGO-Modified MXene Hybrid Films as Multifunctional Electrodes for Hydrogen Evolution and Oxygen Evolution Reactions, Supercapacitors, and DMFC Applications

Exceptional electrical conductivity and abundance of surface terminations like-F- and OH- leading to hydrophilicity make the family of 2D transition metal carbides/nitrides and carbonitrides (MXene) excellent candidates for energy storage and conversion applications. MXenes, however, undergo restacking of nanosheets via van der Waals interaction, hindering the active sites, leading to slow electronic and ionic kinetics, and ultimately affecting their electrochemical performance. Herein, we report binder-free cetyltrimethylammonium bromide-reduced graphene oxide (CTAB-rGO)-modified MXene hybrid films on nickel foam as a promising noble metal-free multifunctional electrode synthesized via layer-by-layer assembly and dip coating techniques, which effectively reduce restacking while improving the kinetics. The properties of the as-prepared electrocatalysts are investigated using various physiochemical characterizations and electrochemical measurements to accomplish the objective of "creating one kind of electrocatalyst for multiapplication" with a thorough understanding of the relationship between the material structure, morphology, and electrocatalytic performance. In energy conversion, the synergetic effect of MXene and the CTAB-rGO support helped increase the catalytic activity of the composite for electrochemical water splitting, demonstrating a current density of 10 mA/cm2 at an overpotential (η) of 360 V and a Tafel slope value of 56.6 mV/dec for hydrogen evolution reaction and a current density of 10 mA/cm2 at an overpotential (η) of 179 mV and a Tafel slope value of 47.03 mV/dec for oxygen evolution reaction in an alkaline medium. The electrode material also exhibited a higher oxidation current density (373.60 mA/cm2) compared to that of synthesized MXene toward methanol oxidation reaction in direct methanol fuel cell application. Additionally, the energy storage potential of CTAB-rGO modified MXene as electrode materials for supercapacitors with a high specific capacitance (544.50 F g-1 at 0.5 A g-1) and a good capacity retention of 87% after 5000 cycles was studied. These findings of this work showcase the potential of the electrocatalyst in both conversion and storage of electrochemical energy.

Influence of coordination structure of Fe-585DV/NxC4-x on the electrocatalytic performance of oxygen reduction reactions

Fe-N-C material, known for its high efficiency, cost-effectiveness, and environmental friendliness, is a promising electrocatalyst in the field of the oxygen reduction reaction (ORR). However, the influence of defects and coordination structures on the catalytic performance of Fe-N-C has not been completely elucidated. In our present investigation, based on density functional theory, we take an Fe adsorbed graphene structure containing a 5-8-5 divacancy (585DV) defect as a research model and investigate the influence of the coordination number of N atoms around Fe (Fe-NxC(4-x)) on the ORR electrocatalyst behavior in alkaline conditions. We find that the Fe-N4 structure exhibits superior ORR catalytic performance than other N coordination structures Fe-NxC4-x (x = 0-3). We explore the reasons for the improved catalytic performance through electronic structure analysis and find that as the N coordination number in the Fe-NxC(4-x) structure increases, the magnetic moment of the Fe single atom decreases. This reduction is conducive to the ORR catalytic performance, indicating that a lower magnetic moment is more favorable for the catalytic process of the ORR within the Fe-NxC(4-x) structure. This study is of great significance for a deeper understanding of the structure-performance relationship in catalysis, as well as for the development of efficient ORR catalysts.

Synergistic Trimetallic Nanocomposites as Visible-NIR-Sunlight-Driven Photocatalysts for Efficient Artificial Photosynthesis

Here, we report monodispersed tricomponent MnNSs-SnO2@Pt and MnNFs-SnO2@Pt nanocomposites prepared by simultaneous SnO2 and Pt nanodot coating on Mn nanospheres (MnNSs) and Mn nanoflowers (MnNFs) for highly efficient CO2 photoreduction in visible-NIR-sunlight irradiation. MnNFs-SnO2@Pt showed higher efficiency with a quantum yield of 3.21% and a chemical yield of 5.45% for CO2 conversion under visible light irradiation for HCOOH formation with 94% selectivity. Similarly, MnNFs-SnO2@Pt displayed significant photocatalytic efficiency in NIR and sunlight irradiation for HCOOH yield. MnNFs-SnO2@Pt nanocomposites also showed robust morphology and sustained structural stability with shelf-life for at least 1 year and were utilized for at least 10 reaction cycles without losing significant photocatalytic efficiency. The high surface area (94.98 m2/g), efficient electron-hole separation, and Pt-nanodot support in MnNFs--SnO2@Pt contributed to a higher photocatalytic efficacy toward CO2 reduction.

Ultrathin Co-N-C Layer Modified Pt-Co Intermetallic Nanoparticles Leading to a High-Performance Electrocatalyst toward Oxygen Reduction and Methanol Oxidation

The development of low platinum-based alloy electrocatalysts is crucial to accelerate the commercialization of fuel cells, yet remains a synthetic challenge and an incompatibility between activity and stability. Herein, a facile procedure to fabricate a high-performance composite that comprises Pt-Co intermetallic nanoparticles (IMNs) and Co, N co-doped carbon (Co-N-C) electrocatalyst is proposed. It is prepared by direct annealing of homemade carbon black-supported Pt nanoparticles (Pt/KB) covered with a Co-phenanthroline complex. During this process, most of Co atoms in the complex are alloyed with Pt to form ordered Pt-Co IMNs, while some Co atoms are atomically dispersed and doped in the framework of superthin carbon layer derived from phenanthroline, which is coordinated with N to form Co-Nx moieties. Moreover, the Co-N-C film obtained from complex is observed to cover the surface of Pt-Co IMNs, which prevent the dissolution and agglomeration of nanoparticles. The composite catalyst exhibits high activity and stability toward oxygen reduction reactions (ORR) and methanol oxidation reactions (MOR), delivering outstanding mass activities of 1.96 and 2.92 A mgPt -1 for ORR and MOR respectively, owing to the synergistic effect of Pt-Co IMNs and Co-N-C film. This study may provide a promising strategy to improve the electrocatalytic performance of Pt-based catalysts.

Orientational Water Bonding on Pt(111): Beyond the Frontier Orbital Principle

For decades, our understanding of water-metal bonding has been dominated by the frontier orbital principle in which globally stable water-metal interactions are ruled by HOMO interacting with metal surfaces. Using density functional theory calculations, herein, we have revealed that the frontier orbital principle cannot be applied to metastable water bonding on Pt(111), where the decisive role of HOMO is replaced by HOMO-1 in terms of the greatest orbital shifts and depopulations as the two different bonding indicators. Unlike the stable water configuration in which both HOMO-1 and HOMO prefer to overlap with metal states through σ-like orbital interactions, metastable configurations exhibit delicate competition or balance between σ-like and π-like orbital interactions exerted by HOMO-1 and HOMO, respectively. These findings have significantly deepened our understanding of orbital roles in water-metal bonding interactions and bridged the gap between theoretical understanding of electrified waters at electrochemical interfaces and water science on metal surfaces.

Amorphous TiOx Stabilized Intermetallic Pt3Ti Nanocatalyst for Methanol Oxidation Reaction

Intermetallic compounds, featuring atomically ordered structures, have emerged as a class of promising electrocatalysts for fuel cells. However, it remains a formidable challenge to controllably synthesize Pt-based intermetallics during the essential high-temperature annealing process as well as stabilize the nanoparticles (NPs) during the electrocatalytic process. Herein, we demonstrated a Ketjen black supported intermetallic Pt₃Ti nanocatalyst coupled with amorphous TiO_x species (Pt₃Ti-TiO_x/KB). The TiO_x can not only confine Pt₃Ti NPs during the synthesis and electrocatalytic process by a strong metal-oxide interaction but also promote the water dissociation for generating more OH species, thus facilitating the conversion of CO_ad. The Pt₃Ti-TiO_x/KB showed a significantly enhanced mass activity (2.15 A mg_Pt^-1) for the methanol oxidation reaction, compared with Pt₃Ti/KB and Pt/C, and presented an impressively high mass activity retention (∼71%) after the durability test. This work provides an effective strategy of coupling Pt-based intermetallics with functional oxides for developing highly performed electrocatalysts.

Activable Ru-PdRu nanosheets with heterogeneous interface for High-efficiency alcohol oxidation reaction

Fabricating 2D nanomaterials with heterogeneous structure is a feasible way to improve catalytic performance owing to its large surface area and tunable electron structure. However, such a category has not been widely reported in the field of alcohol oxidation reaction (AOR). In this work, we reported a new type of heterostructure nanosheet with Ru nanoparticles decorated around the edge of PdRu nanosheets (Ru-PdRu HNSs). Particularly, strong electronic interaction and sufficient active sites attributed to the construction of heterogeneous interface, is the key to the superior electrocatalytic behavior of Ru-PdRu HNSs towards methanol oxidation reaction (MOR), ethylene glycol oxidation reaction (EGOR), and glycerol oxidation reaction (GOR). Remarkably, owing to the enhanced electron transfer brought by the introduction of the Ru-PdRu heterogeneous interface, these novel nanosheets are highly durable. Apart from being able to maintain the highest current density after 4000 s chronoamperometry test, Ru-PdRu HNSs can be reactivated with negligible activity loss in MOR and GOR test after four consecutive i-t experiments. Impressively, in the EGOR test, after reactivation, the current density is step-wisely increased, making it one of the best AOR electrocatalysts.

Trimetallic non-noble NiCoSn alloy as an efficient electrocatalyst towards methanol oxidation and oxygen reduction reactions

The development of a non-noble, highly efficient bifunctional catalyst for methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) is the bottleneck in the alkaline direct methanol fuel cells (ADMFC). Ni-based bi/tri metallic alloys are the promising candidates next to the noble metals in the alkaline medium.Herein we present a facile hydrazine-assisted hydrothermal technique to synthesize a trimetallic nickel-cobalt-tin (NiCoSn) alloy as an efficient electrocatalyst for MOR and ORR reactions. The physiochemical analysis confirms the formation of trimetallic alloys with a high surface area. The as-synthesized trimetallic NiCoSn electrocatalyst exhibited superior MOR activity in terms of mass activity (509 mA mg^-1 at 1.55 V vs RHE) and stability than the bimetallic alloys in 1.0 M KOH electrolyte. Further, the trimetallic alloy delivered a lower onset and half-wave potential of 0.8 and 0.72 V vs RHE with the favorable four-electron transfer in the oxygen reduction reactions. This work highlights a facile approach for preparing Ni-based trimetallic alloys as a promising candidate for the alkaline direct methanol fuel cells/other catalytic applications.

Chemical Surface Grafting of Pt Nanocatalysts for Reconciling Methanol Tolerance with Methanol Oxidation Activity

A conceptual challenge toward more versatile direct methanol fuel cells (DMFCs) is the design of a single material electrocatalyst with high activity and durability for both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). This requires to conciliate methanol tolerance not to hinder ORR at the cathode with a good MOR activity at the anode. This is especially incompatible with Pt materials. We tackled this challenge by deriving a supramolecular concept where surface-grafted molecular ligands regulate the Pt-catalyst reactivity. ORR and MOR activities of newly reported Pt-calix[4]arenes nanocatalysts (Pt CF 3 ${{_{{\rm CF}{_{3}}}}}$ NPs/C) are compared to commercial benchmark PtNPs/C. Pt CF 3 ${{_{{\rm CF}{_{3}}}}}$ NPs/C exhibit a remarkable methanol tolerance without losing the MOR reactivity along with outstanding durability and chemical stability. Beyond designing single-catalyst material, operable in DMFC cathodic and anodic compartments, the results highlight a promising strategy for tuning interfacial properties.

Passivating Oxygen Evolution Activity of NiFe-LDH through Heterostructure Engineering to Realize High-Efficiency Electrocatalytic Formate and Hydrogen Co-Production

An electrocatalytic methanol oxidation reaction (MOR) is proposed to replace oxygen evolution reaction (OER) in water electrolysis owing to the favorable thermodynamics of MOR than OER. However, there is still a competition between the MOR and the OER when the applied potential is in the conventional OER zone. How to inhibit OER while maintaining efficient MOR is an open and challenging question, and there are few reports focusing on this thus far. Herein, by taking NiFe layered double hydroxide (LDH) as a model catalyst due to its intrinsically high catalytic activity for the OER, the perspective of inhibiting OER is shown and thus promoting MOR through a heterogenous engineering of NiFe-LDH. The engineered heterostructure comprising NiFe-LDH and in situ formed NiFe-hexylaminobenzene (NiFe-HAB) coordination polymer exhibits outstanding electrocatalytic capability for methanol oxidation to formic acid (e.g., the Faradaic efficiencies (FEs) of formate product are close to 100% at various current densities, all of which are much larger than those (53-65%) on unmodified NiFe-LDH). Mechanism studies unlock the modification of NiFe-HAB passivates the OER activity of NiFe-LDH through tailoring the free energies for element reaction steps of the OER and increasing the free energy of the rate-determining step, consequently leading to efficient MOR.

Molten Salts Approach of Poly(vinyl alcohol)-Derived Bimetallic Nickel-Iron Sheets Supported on Porous Carbon Nanosheet as an Effective and Durable Electrocatalyst for Methanol Oxidation

The preparation of metallic nanostructures supported on porous carbon materials that are facile, green, efficient, and low-cost is desirable to reduce the cost of electrocatalysts, as well as reduce environmental pollutants. In this study, a series of bimetallic nickel-iron sheets supported on porous carbon nanosheet (NiFe@PCNs) electrocatalysts were synthesized by molten salt synthesis without using any organic solvent or surfactant through controlled metal precursors. The as-prepared NiFe@PCNs were characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction, and photoelectron spectroscopy (XRD and XPS). The TEM results indicated the growth of NiFe sheets on porous carbon nanosheets. The XRD analysis confirmed that the Ni_1-xFe_x alloy had a face-centered polycrystalline (fcc) structure with particle sizes ranging from 15.5 to 30.6 nm. The electrochemical tests showed that the catalytic activity and stability were highly dependent on the iron content. The electrocatalytic activity of catalysts for methanol oxidation demonstrated a nonlinear relationship with the iron ratio. The catalyst doped with 10% iron showed a higher activity compared to the pure nickel catalyst. The maximum current density of Ni_0.9Fe_0.1@PCNs (Ni/Fe ratio 9:1) was 190 mA/cm² at 1.0 M of methanol. In addition to the high electroactivity, the Ni_0.9Fe_0.1@PCNs showed great improvement in stability over 1000 s at 0.5 V with a retained activity of 97%. This method can be used to prepare various bimetallic sheets supported on porous carbon nanosheet electrocatalysts.

One-Step Synthesis of a Non-Precious-Metal Tris (Fe/N/F)-Doped Carbon Catalyst for Oxygen Reduction Reactions

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (2₁P₂-Fe₁-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl₃ as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.

Toward Electrocatalytic Methanol Oxidation Reaction: Longstanding Debates and Emerging Catalysts

The study of direct methanol fuel cells (DMFCs) has lasted around 70 years, since the first investigation in the early 1950s. Though enormous effort has been devoted in this field, it is still far from commercialization. The methanol oxidation reaction (MOR), as a semi-reaction of DMFCs, is the bottleneck reaction that restricts the overall performance of DMFCs. To date, there has been intense debate on the complex six-electron reaction, but barely any reviews have systematically discussed this topic. To this end, the controversies and progress regarding the electrocatalytic mechanisms, performance evaluations as well as the design science toward MOR electrocatalysts are summarized. This review also provides a comprehensive introduction on the recent development of emerging MOR electrocatalysts with a focus on the innovation of the alloy, core-shell structure, heterostructure, and single-atom catalysts. Finally, perspectives on the future outlook toward study of the mechanisms and design of electrocatalysts are provided.

The Role of Bismuth in Suppressing the CO Poisoning in Alkaline Methanol Electrooxidation: Switching the Reaction from the CO to Formate Pathway

While tuning the electronic structure of Pt can thermodynamically alleviate CO poisoning in direct methanol fuel cells, the impact of interactions between intermediates on the reaction pathway is seldom studied. Herein, we contrive a PtBi model catalyst and realize a complete inhibition of the CO pathway and concurrent enhancement of the formate pathway in the alkaline methanol electrooxidation. The key role of Bi is enriching OH adsorbates (OH_ad) on the catalyst surface. The competitive adsorption of CO adsorbates (CO_ad) and OH_ad at Pt sites, complementing the thermodynamic contribution from alloying Bi with Pt, switches the intermediate from CO_ad to formate that circumvents CO poisoning. Hence, 8% Bi brings an approximately 6-fold increase in activity compared to pure Pt nanoparticles. This notion can be generalized to modify commercially available Pt/C catalysts by a microwave-assisted method, offering opportunities for the design and practical production of CO-tolerance electrocatalysts in an industrial setting.

Fast and Versatile Functionalization of Glassy Carbon

A rapid procedure for the functionalization of glassy carbon surfaces (GCSs) is disclosed. A three-step sequence of bromomethylation, azide displacement, and copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) allows ethynylated molecules to be attached covalently to the carbon surface through a methylene functional group. Redox-active ethynyl ferrocene and [Ru^II(Cl)(DMSO)(ethynyl-TPA)]¹⁺ (DMSO = dimethylsulfoxide; TPA = tris(2-pyridylmethyl)amine) are attached with high coverages as assessed by cyclic voltammetry, and the elemental composition of the surface is confirmed by X-ray photoelectron spectroscopy. In less than 1 h, surface coverages of 1 × 10¹⁴ molecules/cm² are possible that exhibit good durability in both acidic and basic media. Attached [Ru^II(Cl)(DMSO)(ethynyl-TPA)]¹⁺ catalytically oxidizes alcohols, yet the currents and potentials are less impressive compared to an attachment without the intervening methylene group. The advantages of this covalent attachment procedure for GCSs are its short reaction times, mild reaction conditions, and the use of standard laboratory reagents and glassware, allowing for many types of ethynylated molecules to be attached rapidly to the surface.

Interface Molecular Functionalization of Cu2O for Synchronous Electrocatalytic Generation of Formate

The electrocatalytic generation of valuable fuels and chemicals from carbon dioxide (CO₂) and others with the assistance of clean solar energy is a highly promising way to realize the carbon-neutral cycle, which invokes the systematic development of advanced electrocatalysts for efficient and selective redox reactions of feedstocks. Herein, we demonstrate the interface modification of cuprous oxide with polyvinylpyrrolidone (PVP) to improve the electrocatalytic efficiency for the synchronous formate generation. Density functional theory calculations reveal that the interfacial properties can be effectively regulated by the PVP functionalization for the favorable formation of intermediates to improve the selectivity of formate generation. Importantly, the advanced electrocatalyts enable an efficient coupling of CO₂ reduction with methanol oxidation in an electrochemical cell powered with a solar cell. The work provides a predictive link between the electrocatalytic redox reactions by applying the interfacial regulation strategies of electrocatalysts.

Pt@Metal-Organic Framework (ZIF-8) Thin Films Obtained at a Liquid/Liquid Interface as Anode Electrocatalysts for Methanol Fuel Cells: Different Approaches in the Synthesis

Smart membranes, nanodevices, chemical sensors, and catalytic coatings are some of the applications that make the metal-organic framework (MOF) thin films very important. Encapsulation of nanoparticles in the porous structure of MOFs can lead to the formation of effective catalysts with new unique properties and wide range of applications that may not be obtained by MOFs individually. Three main strategies, ship-in-a-bottle, bottle-around-the-ship, and in situ synthesis including the simultaneous formation of the two components, were applied for the synthesis of Pt(0)@zeolitic imidazolate framework-8 (ZIF-8) thin films at the toluene/water interface. The effects of platinum precursor transfer directions toward the interface on the properties of the films were investigated by using the [PtCl₂(cod)] (where cod = cis,cis-1,5-cyclooctadiene) complex soluble in toluene as the upper phase and K₂PtCl₄ soluble in water as the lower phase. The six obtained films with different morphologies were applied as electrocatalysts for the methanol oxidation reaction. Considerable current density, mass activity, catalyst stability, activation energy, exchange current density, maximum power, and long-term poisoning rate are some of the advantages of the Pt(0)@ZIF-8 catalysts synthesized using the in situ strategy and K₂PtCl₄ as the platinum precursor. Furthermore, we report the formation of Pt@ZIF-8 nanorods at the interfaces without using any stabilizer or template. Our results suggest that the in situ strategy at the liquid/liquid interface is one of the best procedures for the synthesis of Pt(0)@ZIF-8 thin films as a suitable anode electrocatalyst for methanol fuel cells.

Platinum-Ruthenium Single Atom Alloy as a Bifunctional Electrocatalyst toward Methanol and Hydrogen Oxidation Reactions

The precise regulation for the structural properties of nanomaterials at the atomic scale is an effective strategy to develop high-performance catalysts. Herein, a facile dual-regulation approach was developed to successfully synthesize Ru₁Pt_n single atom alloy (SAA) with atomic Ru dispersed in Pt nanocrystals. High-angle annular dark-field scanning transmission electron microscopy and X-ray absorption fine structure demonstrated that Ru atoms were dispersed in Pt nanocrystals as single atoms. Impressively, the Ru₁Pt_n-SAA exhibited an ultrahigh specific activity (23.59 mA cm^-2) and mass activity (2.805 mA/μg_-PtRu) for methanol oxidation reaction (MOR) and exhibited excellent exchange current density activity (1.992 mA cm^-2) and mass activity (4.71 mA/μg_-PtRu) for hydrogen oxidation reaction (HOR). Density functional theory calculations revealed that the introduction of Ru atoms greatly reduced the reaction free energy for the decomposition of water molecules, which promoted the removal of CO* in the MOR process and adjusted the Gibbs free energy of hydrogen and hydroxyl adsorption to promote the HOR. Our work provided an effective idea for the development of high performance electrocatalysts.

Two-Dimensional Metal-Organic Framework Nanosheets: Synthesis and Applications in Electrocatalysis and Photocatalysis

Two-dimensional metal-organic nanosheets (2D MONs) are an emerging class of ultrathin, porous, and crystalline materials. The organic/inorganic hybrid nature offers MONs distinct advantages over other inorganic nanosheets in terms of diversity of organic ligands and metal notes. Compared to bulk three-dimensional metal-organic frameworks, 2D MONs possess merits of high density and readily accessible catalytic sites, reduced diffusion pathways for reactants/products, and fast electron transport. These features endow MONs with enhanced physical/chemical properties and are ideal for heterogeneous catalysis. In this Review, state-of-the-art synthetic methods for the fabrication of 2D MONs were summarized. The advances of 2D MONs-based materials for electrocatalysis and photocatalysis, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO₂ RR), and electro-/photocatalytic organic transformations were systematically discussed. Finally, the challenges and perspectives regarding future design and synthesis of 2D MONs for high-performance electrocatalysis and photocatalysis were provided.

The catalytic effect of RuM-C catalyst attached to carbon- based support for hydrogen evolution reaction

The potential of converting traditional biomass into low-cost HER catalysts has broad application prospects. In this paper, fungus is used as a carbon-based carrier. The bimetallic catalyst RuM-C (M = V, Mo, W, Zn, Cu) was synthesized under inert gas protection at high temperature. The order of electrocatalytic activity is RuV-C > RuZn-C > RuW-C > RuMo-C > Ru-C > RuCu-C > BF-C, which indicates that RuV-C exhibits excellent HER activity. Due to its irregular sheet structure, the specific surface area of the catalyst is increased. Impressively, it exhibits extremely high catalytic activity for HER in 1 M KOH due to favorable kinetics and excellent specific activity. Consequently, the prepared RuV-C exhibited excellent and stable HER activity compared Ru-C with a low overpotential of 65.78 mV at the current densities of 10 mA cm^-2and Tafel slope of 45.26 mV dec^-1. The potential only decreased by 88 mV after 24 h of continuous testing, which indicates that the catalyst has outstanding stability. This work will provide positive inspiration for the promotion of a new Ru-based biomass HER electrocatalyst.

An Electrochemical Investigation of Methanol Oxidation on Thin Films of Nickel Oxide and Its Composites with Zirconium and Yttrium Oxides

The present work is focused on the fabrication of NiO-ZrO2/FTO and NiO-Y2O3/FTO thin films via a simple dip-coating method. The films are deposited from precursor solutions of Ni(CH3COO)2·2H2O, Zr(CH3COO)4, Y(CH3COO)3·H2O in methanol. The synthesized films, after proper characterization, are employed for electrochemical oxidation of methanol. The analytical techniques such as X-ray diffraction (XRD), Raman, and Infrared (IR) spectroscopy reveal the successful formation of crystalline thin films of mixed metal oxide without any additional impurities. Further, X-ray photoelectron spectroscopy (XPS) results, confirm the composition and oxidation state of all the elements present in thin films. The field emission scanning electron microscopy (FESEM) further aided to identify the uniformity and porous nature of composite thin films while the energy-dispersive X-ray spectroscopy (EDS) confirms the targeted elemental composition of the prepared thin films is in good agreement with precursors. The electrochemical oxidation of methanol results reveals that NiO-Y2O3/FTO and NiO-ZrO2/FTO thin films showed current densities of 6.2 mA/cm2 and 10 mA/cm2 at 0.65 V, respectively, against Ag/AgCl/3M KCl using 0.6 M methanol solution. Furthermore, Chronoamperometric (CA) results show good stability of NiO-ZrO2/FTO and NiO-Y2O3/FTO thin films with observed current decay of 10% and 6.8% of the initial current density, respectively. Moreover, the effect of scan rate and concentration of metals in a catalyst was also investigated. The Electrochemical impedance studies (EIS) further support electrochemical results, where the lower charge transfer resistance (Rct) values are recorded for composite thin films as compared to the pure metal oxide thin films (NiO/FTO, ZrO2/FTO, and Y2O3/FTO).

Pt/Mn3O4 cubes with high anti-poisoning ability for C1 and C2 alcohol fuel oxidation

Pt particles anchored onto Mn₃O₄ cubes were found to have high anti-CO poisoning abilities for C1- and C2-alcohol fuel oxidations in acid electrolyte, due to an electronic effect that enriched the surfaces of the Pt particles with electrons and due to the oxophilicity of Mn₃O₄ in the system.

Finding Key Factors for Efficient Water and Methanol Activation at Metals, Oxides, MXenes, and Metal/Oxide Interfaces

Activating water and methanol is crucial in numerous catalytic, electrocatalytic, and photocatalytic reactions. Despite extensive research, the optimal active sites for water/methanol activation are yet to be unequivocally elucidated. Here, we combine transition-state searches and electronic charge analyses on various structurally different materials to identify two features of favorable O–H bond cleavage in H₂O, CH₃OH, and hydroxyl: (1) low barriers appear when the charge of H moieties remains approximately constant during the dissociation process, as observed on metal oxides, MXenes, and metal/oxide interfaces. Such favorable kinetics is closely related to adsorbate/substrate hydrogen bonding and is enhanced by nearly linear O–H–O angles and short O–H distances. (2) Fast dissociation is observed when the rotation of O–H bonds is facile, which is favored by weak adsorbate binding and effective orbital overlap. Interestingly, we find that the two features are energetically proportional. Finally, we find conspicuous differences between H₂O/CH₃OH and OH activation, which hints toward the use of carefully engineered interfaces.

Ultrafine Rh nanocrystals immobilized on 3D boron and nitrogen co-doped graphene-carbon nanotube networks: high-efficiency electrocatalysts towards methanol oxidation reaction

Rhodium (Rh)-based nanocrystals are recently recognized as promising platinum (Pt)-alternative electrocatalysts for methanol oxidation due to their unique catalytic activity as well as strong anti-poisoning capacity in the alkaline media....

Engineering PtCu nanoparticles for a highly efficient methanol electro-oxidation reaction

Achieving a highly efficient and durable methanol electro-oxidation catalyst in acid media is critical for the practical utilization of direct methanol fuel cells (DMFCs) at the commercial scale. Herein, we report a facile and effective one-pot strategy for the synthesis of carbon-supported PtCu alloy nanoparticles (PtCu NPs) with a Pt-rich surface, small particle size and uniform dispersion. The as-prepared PtCu NPs with the optimal alloy composition (Pt₂Cu) exhibit a significantly improved electrochemical methanol oxidation reaction performance in terms of a high activity, superior CO tolerance and remarkable durability, in contrast to those of commercial Pt/C catalysts in acid media. Particularly, the Pt₂Cu/C catalyst exerts a 4.5 times enhancement in the mass activity and a larger I_f/I_b value compared to those of commercial Pt/C (Pt/C_comm). The enhanced catalytic activities can be ascribed to the high utilization of Pt and the high index facets of the surface. Also, the addition of Cu downshifts the d-band center of Pt and improves the CO tolerance during the methanol oxidation reaction process. This work provides an efficient strategy for designing desired Pt-based alloys for various catalytic reactions.