Atomically Dispersed Copper-Platinum Dual Sites Alloyed with Palladium Nanorings Catalyze the Hydrogen Evolution Reaction

Tailoring Bond Microenvironments and Reaction Pathways of Single-Atom Catalysts for Efficient Water Electrolysis

Single-Atom Sites (SASs) are commonly stabilized and influenced by neighboring atoms in the host; disclosing the structure-reactivity relationships of SASs in water electrolysis are the grand challenges originating from the enormous support materials with complex structures. Through a multidisciplinary view of the design principles, synthesis strategies, characterization techniques, and theoretical analysis of structure-performance correlations, this timely review is dedicated to summarizing the most recent progress in tailoring bond microenvironments on different supports and discussing the reaction pathways and performance advantages of different SAS structures for water electrolysis . The essences and mechanisms of how SAS structures influence their electrocatalysis and the critical needs for their future developments are discussed. Finally, the challenges and perspectives are also provided to stimulate their practically widespread utilization in water-splitting electrolyzers.

In-plane strain engineering in ultrathin noble metal nanosheets boosts the intrinsic electrocatalytic hydrogen evolution activity

Strain has been shown to modulate the electronic structure of noble metal nanomaterials and alter their catalytic performances. Since strain is spatially dependent, it is challenging to expose the active strained interfaces by structural engineering with atomic precision. Herein, we report a facile method to manipulate the planar strain in ultrathin noble metal nanosheets by constructing amorphous-crystalline phase boundaries that can expose the active strained interfaces. Geometric-phase analysis and electron diffraction profile demonstrate the in-plane amorphous-crystalline boundaries can induce about 4% surface tensile strain in the nanosheets. The strained Ir nanosheets display substantially enhanced intrinsic activity toward the hydrogen evolution reaction electrocatalysis with a turnover frequency value 4.5-fold higher than the benchmark Pt/C catalyst. Density functional theory calculations verify that the tensile strain optimizes the d-band states and hydrogen adsorption properties of the strained Ir nanosheets to improve catalysis. Furthermore, the in-plane strain engineering method is demonstrated to be a general approach to boost the hydrogen evolution performance of Ru and Rh nanosheets.

Metal-Organic Frameworks Derived Electrocatalysts for Oxygen and Carbon Dioxide Reduction Reaction

The increasing demands of energy and environmental concerns have motivated researchers to cultivate renewable energy resources for replacing conventional fossil fuels. The modern energy conversion and storage devices required high efficient and stable electrocatalysts to fulfil the market demands. In previous years, we are witness for considerable developments of scientific attention in Metal-organic Frameworks (MOFs) and their derived nanomaterials in electrocatalysis. In current review article, we have discussed the progress of optimistic strategies and approaches for the manufacturing of MOF-derived functional materials and their presentation as electrocatalysts for significant energy related reactions. MOFs functioning as a self-sacrificing template bid different benefits for the preparation of metal nanostructures, metal oxides and carbon-abundant materials promoting through the porous structure, organic functionalities, abundance of metal sites and large surface area. Thorough study for the recent advancement in the MOF-derived materials, metal-coordinated N-doped carbons with single-atom active sites are emerging candidates for future commercial applications. However, there are some tasks that should be addressed, to attain improved, appreciative and controlled structural parameters for catalytic and chemical behavior.

Site-Specified Two-Dimensional Heterojunction of Pt Nanoparticles/Metal-Organic Frameworks for Enhanced Hydrogen Evolution

Heterojunction nanostructures usually exhibit enhanced properties in compariosn with their building blocks and are promising catalyst candidates due to their combined surface and unique interface. Here, for the first time we realized the oriented growth of ultrasmall metal nanoparticles (NPs) on metal-organic framework nanosheets (MOF NSs) by precisely regulating the reduction kinetics of metal ions with solvents. In particular, a rapid reduction of metal ions leads to the random distribution of metal NPs on the surface of MOF NSs, while a slow reduction of metal ions results in the oriented growth of NPs on the edge of MOF NSs. Impressively, the strong synergy between Pt NPs and MOF NSs significantly enhances the hydrogen evolution reaction (HER) performance, and the optimal catalyst displays HER activities superior to those of a composite with a random growth of Pt NPs and commercial Pt/C under both acidic and alkaline conditions. Moreover, the versatility of such oriented growth has been extended to other metal NPs, such as Pd, Ag, and Au. We believe this work will promote research interest in material design for many potential applications.

Low content Ru-incorporated Pd nanowires for bifunctional electrocatalysis

This paper reports the facile synthesis and characterization of carbon supported Pd nanowires with low Ru contents (nRuPd/C). An anti-galvanic replacement reaction involving the reduction of Ru(iii) ions by nanoporous Pd nanowires to form nRuPd alloy nanowires was observed. A series of nRuPd/C materials with various Ru/Pd ratios were prepared by the spontaneous deposition of a Ru cluster on a Pd nanowire core using different Ru precursor concentrations (RuCl₃ = 0.5, 1.0, 5.0 mM). The successful formation of low content Ru-incorporated Pd nanowires without individual Ru clusters were confirmed using physicochemical characterization. The electrocatalytic activity of the nRuPd/C for the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in alkaline media was measured by RDE polarization experiments. The electrocatalytic activity varied greatly depending on the Ru content on the Pd nanowires. Among the catalysts, the prepared Pd nanowires incorporated with a very small amount of Ru (ca. 1.4 wt%) exhibited excellent electrocatalytic activity toward the ORR and HER: positive ORR/HER onset and E_1/2 potentials, higher n value, and lower Tafel slope.

The catalytic activity of Pd nanowires with low Ru contents showed superior bifunctional electrocatalytic performance towards both ORR and HER compared to the benchmarking Pt/C.

Interfacial Electronic Coupling of NC@WO3 -W2 C Decorated Ru Clusters as a Reversible Catalyst toward Electrocatalytic Hydrogen Oxidation and Evolution Reactions

Designing a bifunctional catalyst for hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) is significant toward developing sustainable hydrogen-electric conversion systems. Herein, a cost-effective bifunctional catalyst, Ru/N-doped Carbon@WO₃ -W₂ C (Ru/NC@WOC), was developed via co-precipitation and polyol reduction. Ru/NC@WOC showed superior HOR/HER activity in alkaline solution in comparison with commercial Pt/C. HOR electrochemical tests showed that the mass activity at 0.05 V (1.96  m A μ g R u - 1 ) and exchange-current density were 7.5 and 1.2 times that of Pt/C. Additionality, Ru/NC@WOC exhibited up 30-fold HOR activity in mass activity compared with benchmark Ru/C. Moreover, it also displayed exceptional electrocatalytic HER with overpotentials of 31 mV at 10 mA cm^-2 and 119 mV at 100 mA cm^-2 , surpassing Pt/C, benchmark Ru/C, and most of the previously reported electrocatalysts. The outstanding catalytic activity of Ru/NC@WOC probably arises from the synergy between Ru and NC@WOC matrix, suitable hydrogen binding energy, and highly conductive substrate. Thus, this work may pave a new avenue to fabricate low-cost bifunctional HOR/HER catalysts for alkaline fuel cells and water electrolyzer.

1T-MoS2 Coordinated Bimetal Atoms as Active Centers to Facilitate Hydrogen Generation

Anchoring single metal atoms has been demonstrated as an effective strategy to boost the catalytic performance of non-noble metal 1T-MoS₂ towards hydrogen evolution reaction (HER). However, the dual active sites on 1T-MoS₂ still remain a great challenge. Here, first-principles calculations were performed to systematically investigate the electrocatalytic HER activity of single and dual transition metal (TM) atoms bound to the 1T-MoS₂ monolayer (TM@1T-MoS₂). The resulted Ti@1T-MoS₂ exhibits excellent structural stability, near-thermoneutral adsorption of H* and ultralow reaction barrier (0.15 eV). It is a promising single metal atom catalyst for HER, outperformed the reported Co, Ni and Pd anchoring species. Surprisingly, by further introducing Pd atoms coordinated with S atoms or S vacancies on the Ti@1T-MoS₂ surface, the resulted catalyst not only maintains the high HER activity of Ti sites, but also achieves new dual active moiety due to the appropriate H* adsorption free energy on Pd sites. This work is of great significance for realizing dual active centers on 1T-MoS₂ nanosheets and offers new thought for developing high-performance electrocatalysts for HER.

Bimetal CoNi Active Sites on Mesoporous Carbon Nanosheets to Kinetically Boost Lithium-Sulfur Batteries

In order to solve the problem that soluble polysulfide intermediates diffuse between cathode and anode during charging and discharging, which leads to rapid attenuation of battery cycle life, the separator modification materials come into people's sight. Herein, a mesoporous carbon-supported cobalt-nickel bimetal composite (CoNi@MPC) is synthesized and directly coated on the original separator to serve as a secondary collector for lithium-sulfur batteries. CoNi@MPC exhibits multiple Co-Ni active sites, able to catalyze the reactions of soluble polysulfides, specifically accelerating the generation and decomposition of insoluble Li₂ S in lithiation and delithiation process testified by the electrochemical results and density functional theory calculation. Relying on the bifunctionality of CoNi@MPC composite, the shuttle effect of lithium polysulfides can be effectively alleviated. Moreover, porous carbon as the conductive scaffold favors the improvement of electronic conductivity. Benefiting from the above advantages, the cell with CoNi@MPC separator indicates significantly enhanced electrochemical performances with excellent cycling life over 500 cycles and superior rate capabilities.

Synthesis of raspberry-like antimony-platinum (SbPt) nanoparticles as highly active electrocatalysts for hydrogen evolution reaction

Binary transition metals can facilitate the hydrogen evolution reaction (HER) through the synergistic integration of different electrochemical properties. To determine binary transition metals that are highly active, Greely et al. conducted a simulation of 256 different binary transition metals. They demonstrated that BiPt, PtRu, AsPt, SbPt, BiRh, RhRe, PtRe, AsRu, IrRu, RhRu, IrRe, and PtRh could be used as efficient electrocatalysts for HER. However, only few of them are synthesized and used as electrocatalysts. In this work, we report the synthesis of the raspberry-like antimony-platinum (SbPt) nanoparticles (NPs) via a colloidal nanocrystal synthesis. These NPs exhibited efficient activity with a low overpotential of 27 mV to reach 10 mA cm^-2 in acidic media. We conducted long-term durability test for 90,000 s under an applied voltage of 0.5 V (vs. RHE) and cycling tests of over 10,000 cycles under an applied voltage of 0.1 to -0.5 V (vs. RHE). The high activity exhibited by the raspberry-like SbPt NPs may be due to the following reasons: (1) the raspberry-like SbPt NPs exhibited versatile active exposed (110), (100), (101), and (012) facets as efficient HER catalysts, and (2) as confirmed by both the density functional theory (DFT) simulation and experimental results, the presence of Sb 3d subsurface broadened the Pt surface d-band, which caused synergistic effects on water splitting. In summary, synthesis of the new colloidal raspberry-like SbPt NPs is essential to elucidate the fundamental properties of the nanomaterial and nanostructure design. This study could facilitate the development of Pt-group materials that can be used as HER catalysts.

Polyvinylpyrrolidone-Coordinated Single-Site Platinum Catalyst Exhibits High Activity for Hydrogen Evolution Reaction

The essence of developing a Pt-based single-atom catalyst (SAC) for hydrogen evolution reaction (HER) is the preparation of well-defined and stable single Pt sites with desired electrocatalytic efficacy. Herein, we report a facile approach to generate uniformly dispersed Pt sites with outstanding HER performance via a photochemical reduction method using polyvinylpyrrolidone (PVP) molecules as the key additive to significantly simplify the synthesis and enhance the catalytic performance. The as-prepared catalyst displays remarkable kinetic activities (20 times higher current density than the commercially available Pt/C) with excellent stability (76.3 % of its initial activity after 5000 cycles) for HER. EXAFS measurements and DFT calculations demonstrate a synergetic effect, where the PVP ligands and the support together modulate the electronic structure of the Pt atoms, which optimize the hydrogen adsorption energy, resulting in a considerably improved HER activity.

Intrinsic Effect of Carbon Supports on the Activity and Stability of Precious Metal Based Catalysts for Electrocatalytic Alcohol Oxidation in Fuel Cells: A Review

Electrocatalyst supports, in particular carbonaceous materials, play critical roles in the electrocatalytic activity and stability of precious metal group (PMG)-based catalysts such as Pt, Pd, and Au for the electrochemical alcohol oxidation reaction (AOR) of fuels such as methanol and ethanol in polymer electrolyte membrane fuel cells (PEMFCs). Carbonaceous supports such as high surface area carbon provide electronic contact throughout the catalyst layer, isolate PMG nanoparticles (NPs) to maintain high electrochemical surface area, and provide hydrophobic properties to avoid flooding of the catalyst layer by liquid water produced. Compared to high surface area carbon, PMG catalysts supported on 1D and 2D carbon materials such as graphene and carbon nanotubes show enhanced activity and durability due to the intrinsic effect of the underlying carbonaceous supports on the electronic states of PMG NPs. The modification of the electronic environment, in particular the d-band centers of PMG NPs, weakens the adsorption of AOR intermediates, facilitates breaking of the C-C bonds, and thus enhances the electrocatalytic activity of PMG catalysts. The doping of heteroatoms further facilitates the electrocatalytic activity for the AOR through the structural, bifunctional, and electronic effects, in addition to the enhanced dispersion of PMG NPs in the carbon support. The prospects for the development of effective PMG-based catalysts for high-performance alcohol-fuel-based PEMFCs is discussed.

Atomically Dispersed Pt on Screw-like Pd/Au Core-shell Nanowires for Enhanced Electrocatalysis

Engineering noble metal nanostructures at the atomic level can significantly optimize their electrocatalytic performance and remarkably reduce their usage. We report the synthesis of atomically dispersed Pt on screw-like Pd/Au nanowires by using ultrafine Pd nanowires as seeds. Au can selectively grow on the surface of Pd nanowires by an island growth pattern to fabricate surface defect sites to load atomically dispersed Pt, which can be confirmed by X-ray absorption fine structure measurements and aberration corrected HRTEM images. The nanowires with 2.74 at % Pt exhibit superior HER properties in acidic solution with an overpotential of 20.6 mV at 10 mA cm^-2 and enhanced alkaline ORR performance with a mass activity over 15 times greater than the commercial platinum/carbon (Pt/C) catalysts.

In Situ Formed Pt3Ti Nanoparticles on a Two-Dimensional Transition Metal Carbide (MXene) Used as Efficient Catalysts for Hydrogen Evolution Reactions

The design of efficient catalysts capable of delivering high currents at low overpotentials for hydrogen evolution reactions (HERs) is urgently needed to use catalysts in practical applications. Herein, we report platinum (Pt) alloyed with titanium (Ti) from the surface of Ti₃C₂T_x MXenes to form Pt₃Ti intermetallic compound (IMC) nanoparticles (NPs) via in situ coreduction. In situ X-ray absorption spectroscopy (XAS) indicates that Pt undergoes a temperature-dependent transformation from single atoms to intermetallic compounds, and the catalyst reduced at 550 °C exhibits a superior HER performance in acidic media. The Pt/Ti₃C₂T_x-550 catalyst outperforms commercial Pt/Vulcan and has a small overpotential of 32.7 mV at 10 mA cm^-2 and a low Tafel slope of 32.3 mV dec^-1. The HER current was normalized by the mass and dispersion of Pt, and the mass activity and specific activity of Pt/Ti₃C₂T_x-550 are 4.4 and 13 times higher, respectively, than those of Pt/Vulcan at an overpotential of 70 mV. The density functional theory (DFT) calculations suggest that the (111)- and (100)-terminated Pt₃Ti nanoparticles exhibit *H binding comparable to Pt(111), while the (110) termination has an *H adsorption that is too exergonic, thus poisoned in the low overpotential region. This work demonstrates the potential of MXenes as platforms for the design of electrocatalysts and may spur future research for other MXene-supported metal catalysts that can be used for a wide range of electrocatalytic reactions.

Creating cross-linked lamellar block copolymer supporting layers for biomimetic membranes

The long-standing goal in membrane development is creating materials with superior transport properties, including both high flux and high selectivity. These properties are common in biological membranes, and thus mimicking nature is a promising strategy towards improved membrane design. In previous studies, we have shown that artificial water channels can have excellent water transport abilities that are comparable to biological water channel proteins, aquaporins. In this study, we propose a strategy for incorporation of artificial channels that mimic biological channels into stable polymeric membranes. Specifically, we synthesized an amphiphilic triblock copolymer, poly(isoprene)-block-poly(ethylene oxide)-block-poly(isoprene), which is a high molecular weight synthetic analog of naturally occurring lipids in terms of its self-assembled structure. This polymer was used to build stacked membranes composed of self-assembled lamellae. The resulting membranes resemble layers of natural lipid bilayers in living systems, but with superior mechanical properties suitable for real-world applications. The procedures used to synthesize the triblock copolymer resulted in membranes with increased stability due to the crosslinkability of the hydrophobic domains. Furthermore, the introduction of bridging hydrophilic domains leads to the preservation of the stacked membrane structure when the membrane is in contact with water, something that is challenging for diblock lamellae that tend to swell, and delaminate in aqueous solutions. This new method of membrane fabrication offers a practical model for making channel-based biomimetic membranes, which may lead to technological applications in reverse osmosis, nanofiltration, and ultrafiltration membranes.

Support and Interface Effects in Water-Splitting Electrocatalysts

Water-splitting electrolyzers that can convert electricity into storable hydrogen are a fascinating and scalable energy conversion technology for the utilization of renewable energies. To speed up the sluggish hydrogen and oxygen evolution reactions (HER and OER), electrocatalysts are essential for reducing their kinetic energy barriers and eventually improving the energy conversion efficiency. As efficient strategies for modulating the binding ability of water-splitting intermediates on electrocatalyst surface, the support effect and interface effect are drawing growing attention. Herein, some of the recent research progress on the support and interface effects in HER, OER, and overall water-splitting electrocatalysts is highlighted. Specifically, the correlation between the electronic interaction of the constituent components and the electrocatalytic water-splitting performance of electrocatalysts is profoundly discussed, with the aim of advancing the development of highly efficient water-splitting electrocatalysts, which may eventually replace the noble-metal-based electrocatalysts and bring the practically widespread utilization of water-splitting electrolyzers into a reality.

Nonmetal Doping as a Robust Route for Boosting the Hydrogen Evolution of Metal-Based Electrocatalysts

Recently, nonmetal doping has exhibited its great potential for boosting the hydrogen evolution reaction (HER) of transition-metal (TM)-based electrocatalysts. To this end, this work overviews the recent achievements made on the design and development of the nonmetal-doped TM-based electrocatalysts and their performance for the HER. It is also shown that by rationally doping nonmetal elements, the electronic structures of TM-based electrocatalysts can be effectively tuned and in turn the Gibbs free energy of the TM for adsorption of H* intermediates (ΔG_H* ) optimized, consequently enhancing the intrinsic activity of TM-based electrocatalysts. Notably, we highlight that concurrently doping two nonmetal elements can continuously and precisely regulate the electronic structures of the TM, thereby maximizing the activity for HER. Moreover, nonmetal doping also accounts for enhancing the physical properties of the TM (i.e. surface area). Therefore, nonmetal doping is a robust strategy for simultaneous regulation of the chemical and physical features of the TM.

Electrochemical Hydrogen Evolution Reaction Efficiently Catalyzed by Ru2 P Nanoparticles

Developing alternatives to Pt catalysts is a prerequisite to cost-effectively produce hydrogen. Herein, we demonstrate Ru₂ P nanoparticles (without any doping and modifications) as a highly efficient Pt-like catalyst for the hydrogen evolution reaction (HER) in different pH electrolytes. On transferring the hexagonal close-packed crystal structure of Ru to the orthorhombic structure of Ru₂ P, a greatly improved catalytic activity and stability toward HER is found owing to Ru-P coordination. The electronic state change originates from the P-Ru bonding structures, which accounts for the HER activity improvement compared with Ru nanoparticles. Specifically, Ru₂ P nanoparticles can drive 10 mA cm^-2 at a very low overpotential of 55 mV, only 8 mV more than Pt/C in an acidic solution; and an extremely low overpotential of approximately 50 mV is needed in alkaline solution, about 20 mV less than the Pt/C catalyst. The Volmer-Tafel mechanism is indicated on Ru₂ P nanoparticles with the typical Tafel slope of 30 mV dec^-1 of Pt metal indicating a Pt-like catalytic ability. Ru₂ P is more active in the Ru-P family as H atoms prefer to adsorb on Ru atoms rather than on the P element according to theoretical calculations. Considering the low price of Ru (20 % of Pt), anti-corrosion ability in the electrolyte, and the safe and reliable fabrication approach, the powder Ru₂ P nanoparticles make an excellent HER catalyst with great promise for large-scale water electrolysis applications.