A Biphasic Strategy to Synergistically Accelerate Activation and CO Spillover in Formic Acid Oxidation Catalysis.

Developing highly efficient and carbon monoxide (CO)-tolerant platinum (Pt) catalysts for the formic acid oxidation reaction (FAOR) is vital for direct formic acid fuel cells (DFAFCs), yet it is challenging due to the high energy barrier of direct intermediates (HCOO* and COOH*) as well as the CO poisoning issues associated with Pt alloy catalysts. Here we present a versatile biphasic strategy by creating a hexagonal/cubic crystalline-phase-synergistic PtPb/C (h/c-PtPb/C) catalyst to tackle the aforementioned issues. Detailed investigations reveal that h/c-PtPb/C can simultaneously facilitate the adsorption of direct intermediates while inhibiting CO adsorption, thereby significantly improving the activation and CO spillover. As a result, h/c-PtPb/C showcases an outstanding FAOR activity of 8.1 A mgPt-1, which is 64.5 times higher than that of commercial Pt/C and significantly surpasses monophasic PtPb. Moreover, the h/c-PtPb/C-based membrane electrode assembly exhibits an exceptional peak power density of 258.7 mW cm-2 for practical DFAFC applications.

3D Noble-Metal Nanostructures Approaching Atomic Efficiency and Atomic Density Limits.

Noble metals have been widely used in catalysis, however, the scarcity and high cost of noble metal motivate researchers to balance the atomic efficiency and atomic density, which is formidably challenging. This article proposes a robust strategy for fabricating 3D amorphous noble metal-based oxides with simultaneous enhancement on atomic efficiency and density with the assistance of atomic channels, where the atomic utilization increases from 18.2% to 59.4%. The unique properties of amorphous bimetallic oxides and formation of atomic channels have been evidenced by detailed experimental characterizations and theoretical simulations. Moreover, the universality of the current strategy is validated by other binary oxides. When Cu2IrOx with atomic channels (Cu2IrOx-AE) is used as catalyst for oxygen evolution reaction (OER), the mass activity and turnover frequency value of Cu2IrOx-AE are 1-2 orders of magnitude higher than CuO/IrO2 and Cu2IrOx without atomic channels, largely outperforming the reported OER catalysts. Theoretical calculations reveal that the formation of atomic channels leads to various Ir sites, on which the proton of adsorbed *OH can transfer to adjacent O atoms of [IrO6]. This work may attract immediate interest of researchers in material science, chemistry, catalysis, and beyond.

Compressive Strain in Platinum-Iridium-Nickel Zigzag-Like Nanowire Boosts Hydrogen Catalysis.

Strain effect in the structurally defective materials can contribute to the catalysis optimization. However, it is challenging to achieve the performance improvement by strain modulation with the help of geometrical structure because strain is spatially dependent. Here, a new class of compressively strained platinum-iridium-metal zigzag-like nanowires (PtIrM ZNWs, M = nickel (Ni), cobalt (Co), iron (Fe), zinc (Zn) and gallium (Ga)) is reported as the efficient alkaline hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) catalysts. Particularly, the optimized PtIrNi ZNWs with 3% compressive strain (cs-PtIrNi ZNWs) can achieve the highest HER/HOR performances among all the catalysts investigate. Their HOR mass and specific activities are 3.2/14.4 and 2.6/32.7 times larger than those of PtIrNi NWs and commercial Pt/C, respectively. Simultaneously, they can exhibit the superior stability and high CO resistance for HOR. Further, experimental and theoretical studies collectively reveal that the compressive strain in cs-PtIrNi ZNWs effectively weakens the adsorption of hydroxyl intermediate and modulates the electronic structure, resulting in the weakened hydrogen binding energy (HBE) and moderate hydroxide binding energy (OHBE), beneficial for the improvement of HOR performance. This work highlights the importance of strain tuning in enhancing Pt-based nanomaterials for hydrogen catalysis and beyond.

Continuous Phase Regulation of a Pd-Te Hexagonal Nanoplate Library.

Phase regulation of noble metal-based nanomaterials provides a promising strategy for boosting the catalytic performance. However, realizing the continuous phase modulation in two-dimensional structures and unveiling the relevant structure-performance relationship remain significant challenges. In this work, we present the first example of continuous phase modulation in a library of Pd-Te hexagonal nanoplates (HNPs) from cubic-phase Pd4Te, rhombohedral-phase Pd20Te7, rhombohedral-phase Pd8Te3, and hexagonal-phase PdTe to hexagonal-phase PdTe2. Notably, the continuous phase regulation of the well-defined Pd-Te HNPs enables the successful modulation of the distance between adjacent Pd active sites, triggering an exciting way for tuning the relevant catalytic reactions intrinsically. The proof-of-concept oxygen reduction reaction (ORR) experiment shows a Pd-Pd distance-dependent ORR performance, where the hexagonal-phase PdTe HNPs present the best electrochemical performance in ORR (mass activity and specific activity of 1.02 A mg-1Pd and 1.83 mA cm-2Pd at 0.9 V vs RHE). Theoretical investigation reveals that the increased Pd-Pd distance relates to the weak *OH adsorption over Pd-Te HNPs, thus contributing to the remarkable ORR activity of PdTe HNPs. This work advances the phase-controlled synthesis of noble metal-based nanostructures, which gives huge impetus to the design of high-efficiency nanomaterials for diverse applications.

PtNi/PtIn-Skin Fishbone-Like Nanowires Boost Alkaline Hydrogen Oxidation Catalysis.

The development of high-performance platinum (Pt)-based electrocatalysts for the hydrogen oxidation reaction (HOR) is highly desirable for hydrogen fuel cells, but it is limited by the sluggish kinetics and severe carbon monoxide (CO) poisoning in alkaline medium. Herein, we explore a class of facet-selected Pt-nickel-indium fishbone-like nanowires (PtNiIn FNWs) featuring high-index facets (HIFs) of Pt3In skin as efficient alkaline HOR catalysts. Impressively, the optimized Pt66Ni6In28 FNWs show the highest mass and specific activities of 4.02 A mgPt-1 and 6.56 mA cm-2, 2.0/2.1 and 13.9/15.6 times larger than those of commercial PtRu/C and commercial Pt/C, respectively, along with a competitive CO-tolerance ability. Specifically, they exhibit only 6.0% current density decay after 10000 s of operation and 25.7% activity loss after 2000 s in the presence of 1000 ppm of CO. Moreover, an isotope experiment and density functional theory (DFT) calculations further prove that the unique structure and synergy among Pt, Ni, and In endow these Pt66Ni6In28 FNWs with an optimized hydrogen binding energy (HBE) and an advantageous hydroxide binding energy (OHBE), giving them excellent alkaline HOR properties. The combined construction of surface-skin and HIFs in PtNiIn FNWs will offer an available method to realize the potential applications of advanced non-PtRu-based catalysts in fuel cells and beyond.

Pb-Modified Ultrathin RuCu Nanoflowers for Active, Stable, and CO-resistant Alkaline Electrocatalytic Hydrogen Oxidation.

CO poisoning of Pt group metal (PGM) catalysts is a chronic problem for hydrogen oxidation reaction (HOR), the anodic reaction of hydroxide exchange membrane fuel cell (HEMFC) for converting H2 to electric energy in sustainable manner. We demonstrate here an ultrathin Ru-based nanoflower modified with Pb (PbRuCu NF) as an active, stable, and CO-resistant catalyst for alkaline HOR. Mechanism studies show that the presence of Pb can weaken the adsorption of *H, strengthen *OH adsorption to facilitate CO oxidation, as a result of significantly enhanced HOR activity and improved CO tolerance. Furthermore, in situ electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) suggests that Pb acts as oxygen-rich site to regulate the behavior of the linear CO adsorption. The optimized Pb1.04 -Ru92 Cu8 /C displays a mass activity and specific activity of 1.10 A mgRu -1 and 5.55 mA cm-2 , which are ≈10 and ≈31 times higher than those of commercial Pt/C. This work provides a facile strategy for the design of Ru-based catalyst with high activity and strong CO-resistance for alkaline HOR, which may promote the fundamental researches on the rational design of functional catalysts.

Sub-Monolayer SbOx on PtPb/Pt Nanoplate Boosts Direct Formic Acid Oxidation Catalysis.

To promote the commercialization of direct formic acid fuel cell (DFAFC), it is vital to explore new types of direct formic acid oxidation (FAOR) catalysts with high activity and direct pathway. Here, we report the synthesis of intermetallic platinum-lead/platinum nanoplates inlaid with sub-monolayer antimony oxide surface (PtPb/Pt@sub-SbOx NPs) for efficient catalytic applications in FAOR. Impressively, they can achieve the remarkable FAOR specific and mass activities of 28.7 mA cm-2 and 7.2 A mgPt-1, which are 151 and 60 times higher than those of the state-of-the-art commercial Pt/C, respectively. Furthermore, the X-ray photoelectron spectroscopy and X-ray absorption spectroscopy results collectively reveal the optimization of the local coordination environment by the surface sub-monolayer SbOx, along with the electron transfer from Pb and Sb to Pt, driving the predominant dehydrogenation process. The sub-monolayer SbOx on the surface can effectively attenuate the CO generation, largely improving the FAOR performance of PtPb/Pt@sub-SbOx NPs. This work develops a class of high-performance Pt-based anodic catalyst for DFAFC via constructing the unique intermetallic core/sub-monolayer shell structure.

Highly Selective Synthesis of Monoclinic-Phased Platinum-Tellurium Nanotrepang for Direct Formic Acid Oxidation Catalysis.

Designing efficient formic acid oxidation reaction (FAOR) catalysts with remarkable membrane electrode assembly (MEA) performance in a direct formic acid fuel cell (DFAFC) medium is significant yet challenging. Herein, we report that the monoclinic-phased platinum-tellurium nanotrepang (m-PtTe NT) can be adopted as a highly active, selective, and stable FAOR catalyst with a desirable direct reaction pathway. The m-PtTe NT exhibits the high specific and mass activities of 6.78 mA cm-2 and 3.2 A mgPt-1, respectively, which are 35.7/22.9, 2.8/2.6, and 3.9/2.9 times higher than those of commercial Pt/C, rhombohedral-phased Pt2Te3 NT (r-Pt2Te3 NT), and trigonal-phased PtTe2 NT (t-PtTe2 NT), respectively. Simultaneously, the highest reaction tendency for the direct FAOR pathway and the best tolerance to poisonous CO intermediate can also be realized by m-PtTe NT. More importantly, even in a single-cell medium, the m-PtTe NT can display a much higher MEA power density (171.4 mW cm-2) and stability (53.2% voltage loss after 5660 s) than those of commercial Pt/C, demonstrating the great potential in operating DFAFC device. The in-situ Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy jointly demonstrate that the unique nanostructure of m-PtTe NT can effectively optimize dehydrogenation steps and inhibit the CO intermediate adsorption, as well as promote the oxidation of noxious CO intermediate, thus achieving the great improvement of FAOR activity, poisoning tolerance, and stability. Density functional theory calculations further reveal that the direct pathway is the most favorable on m-PtTe NT than r-Pt2Te3 NT and t-PtTe2 NT. The higher activation energy to produce CO and the relatively weaker binding with CO of m-PtTe NT result in the better CO tolerance. This work achieves remarkable FAOR and MEA performances of advanced Pt-based anodic catalysts for DFAFCs via a phase engineering strategy.

Platinum-Lead-Bismuth/Platinum-Bismuth Core/Shell Nanoplate Achieves Complete Dehydrogenation Pathway for Direct Formic Acid Oxidation Catalysis.

Designing platinum (Pt)-based formic acid oxidation reaction (FAOR) catalysts with high performance and high selectivity of direct dehydrogenation pathway for direct formic acid fuel cell (DFAFC) is desirable yet challenging. Herein, we report a new class of surface-uneven PtPbBi/PtBi core/shell nanoplates (PtPbBi/PtBi NPs) as the highly active and selective FAOR catalysts, even in the complicated membrane electrode assembly (MEA) medium. They can achieve unprecedented specific and mass activities of 25.1 mA cm-2 and 7.4 A mgPt-1 for FAOR, 156 and 62 times higher than those of commercial Pt/C, respectively, which is the highest for a FAOR catalyst by far. Simultaneously, they show highly weak adsorption of CO and high dehydrogenation pathway selectivity in the FAOR test. More importantly, the PtPbBi/PtBi NPs can reach the power density of 161.5 mW cm-2, along with a stable discharge performance (45.8% decay of power density at 0.4 V for 10 h), demonstrating great potential in a single DFAFC device. The in situ Fourier transform infrared spectroscopy (FTIR) and X-ray absorption spectroscopy (XAS) results collectively reveal a local electron interaction between PtPbBi and PtBi. In addition, the high-tolerance PtBi shell can effectively inhibit the production/adsorption of CO, resulting in the complete presence of the dehydrogenation pathway for FAOR. This work demonstrates an efficient Pt-based FAOR catalyst with 100% direct reaction selectivity, which is of great significance for driving the commercialization of DFAFC.

Interfacial Synergy between the Cu Atomic Layer and CeO2 Promotes CO Electrocoupling to Acetate.

Cu is considered to be an effective electrocatalyst in CO/CO2 reduction reactions (CORR/CO2RR) because of its C-C coupling into C2+ products, but it still remains a formidable challenge to rationally design Cu-based catalysts for highly selective CO/CO2 reduction to C2+ liquid products such as acetate. We here demonstrate that spraying atomically layered Cu atoms onto CeO2 nanorods (Cu-CeO2) can lead to a catalyst with an enhanced acetate selectivity in CORR. Owing to the existence of oxygen vacancies (Ov) in CeO2, the layer of Cu atoms at interface coordinates with Ce atoms in the form of Cu-Ce (Ov), as a result of strong interfacial synergy. The Cu-Ce (Ov) significantly promotes the adsorption and dissociation of H2O, which further couples with CO to selectively produce acetate as the dominant liquid product. In the current density range of 50-150 mA cm-2, the Faradaic efficiencies (FEs) of acetate are over 50% with a maximum value of 62.4%. In particular, the turnover frequency of Cu-CeO2 reaches 1477 h-1, surpassing that of Cu nanoparticle-decorated CeO2 nanorods, bare CeO2 nanorods, as well as other existing Cu-based catalysts. This work advances the rational design of high-performance catalysts for CORR to highly value-added products, which may attract great interests in diverse fields including materials science, chemistry, and catalysis.

Low-Coordination Trimetallic PtFeCo Nanosaws for Practical Fuel Cells.

Developing high-performance catalysts for fuel cell catalysis is the most critical and challenging step for the commercialization of fuel cell technology. Here 1D trimetallic platinum-iron-cobalt nanosaws (Pt3 FeCo NSs) with low-coordination features are designed as efficient bifunctional electrocatalysts for practical fuel cell catalysis. The oxygen reduction reaction (ORR) activity of Pt3 FeCo NSs (10.62 mA cm-2 and 4.66 A mg-1 Pt at 0.90 V) is more than 25-folds higher than that of the commercial Pt/C, even after 30 000 voltage cycles. Density functional theory calculations reveal that the strong inter-d-orbital electron transfer minimizes the ORR barrier with higher selectivity at robust valence states. The volcano correlation between the intrinsic structure featured with low-coordination Pt-sites and corresponding electronic activities is discovered, which guarantees high ORR activities. The Pt3 FeCo NSs located in the membrane electrode assembly (MEA) also achieve very high peak power density (1800.6 mW cm-2 ) and competitive specific/mass activities (1.79 mA cm-2 and 0.79 A mg-1 Pt at 0.90 ViR-free cell voltage) as well as a long-term lifetime in specific H2 O2 medium for proton-exchange-membrane fuel cells, ranking top electrocatalysts reported to date for MEA. This work represents a class of multimetallic Pt-based nanocatalysts for practical fuel cells and beyond.

Medium/High-Entropy Amalgamated Core/Shell Nanoplate Achieves Efficient Formic Acid Catalysis for Direct Formic Acid Fuel Cell.

High-entropy alloys (HEAs) have been attracting extensive research interests in designing advanced nanomaterials, while their precise control is still in the infancy stage. Herein, we have reported a well-defined PtBiPbNiCo hexagonal nanoplates (HEA HPs) as high-performance electrocatalysts. Structure analysis decodes that the HEA HP is constructed with PtBiPb medium-entropy core and PtBiNiCo high-entropy shell. Significantly, the HEA HPs can reach the specific and mass activities of 27.2 mA cm-2 and 7.1 A mgPt -1 for formic acid oxidation reaction (FAOR), being the record catalyst ever achieved in Pt-based catalysts, and can realize the membrane electrode assembly (MEA) power density (321.2 mW cm-2 ) in fuel cell. Further experimental and theoretical analyses collectively evidence that the hexagonal intermetallic core/atomic layer shell structure and multi-element synergy greatly promote the direct dehydrogenation pathway of formic acid molecule and suppress the formation of CO*.

Subnanometer high-entropy alloy nanowires enable remarkable hydrogen oxidation catalysis.

High-entropy alloys (HEAs) with unique physicochemical properties have attracted tremendous attention in many fields, yet the precise control on dimension and morphology at atomic level remains formidable challenges. Herein, we synthesize unique PtRuNiCoFeMo HEA subnanometer nanowires (SNWs) for alkaline hydrogen oxidation reaction (HOR). The mass and specific activities of HEA SNWs/C reach 6.75 A mgPt+Ru-1 and 8.96 mA cm-2, respectively, which are 2.8/2.6, 4.1/2.4, and 19.8/18.7 times higher than those of HEA NPs/C, commercial PtRu/C and Pt/C, respectively. It can even display enhanced resistance to CO poisoning during HOR in the presence of 1000 ppm CO. Density functional theory calculations reveal that the strong interactions between different metal sites in HEA SNWs can greatly regulate the binding strength of proton and hydroxyl, and therefore enhances the HOR activity. This work not only provides a viable synthetic route for the fabrication of Pt-based HEA subnano/nano materials, but also promotes the fundamental researches on catalysis and beyond.

Triple hierarchy and double synergies of NiFe/Co9S8/carbon cloth: a new and efficient electrocatalyst for the oxygen evolution reaction.

Electrochemical water splitting requires an efficient water oxidation catalyst to accelerate the oxygen evolution reaction (OER). A triple hierarchy catalyst structure based on abundant transition metals in soil (Fe, Co, and Ni) was prepared via chemical bath deposition, followed by a hydrothermal and electrodeposition method for the high-efficiency OER. The obtained electrode consisted of a three-layer porous structure, with a carbon cloth (CC) substrate as the bottom layer, vertically aligned Co9S8 nanotubes as the intermediate layer, and NiFe hydroxide as the top layer, resulting in two synergistic effects between Co9S8 and CC, and NiFe and Co9S8. This layered structure contained no binder, which facilitated catalytic site exposure, enhanced electron transfer, and accelerated the dissipation of gases generated during the catalytic process. This triple hierarchy multimetal/carbon electrode exhibited remarkable OER activity in an alkaline medium with a small overpotential of 219 mV (vs. RHE) at 10 mA·cm-2 and low Tafel slope of 55 mV·dec-1. Furthermore, this triple hierarchy electrode was stable for up to 20 h. The prepared triple hierarchy polymetallic material can be considered to be among the most promising oxygen evolution catalysts.