Coherent hexagonal platinum skin on nickel nanocrystals for enhanced hydrogen evolution activity

Pd hydride metallene aerogels with lattice hydrogen participation for efficient hydrogen evolution reaction

Hydrogen adsorption and desorption in single-phase catalysts often occur at a single catalytic site based on the traditional hydrogen evolution reaction (HER) pathway, which makes it difficult to break the limitation entailed by the Sabatier principle. Herein, β-Pd hydride metallene (β-PdHene) aerogels are synthesized as advanced HER catalysts. A lattice hydrogen-involved mechanism is reported to separate adsorption and desorption sites, which is thermodynamically favorable compared to the traditional reaction pathway. In situ differential electrochemical mass spectrometry and theoretical calculations reveal that lattice hydrogen as additional active sites directly participate in the HER process. Consequently, β-PdHene aerogels exhibit a low overpotential of only 20 mV at 10 mA cm-2 and remarkable HER stability, which are even comparable to commercial Pt/C. Our work opens an avenue to rationally develop highly active HER catalysts, bypassing the design limitations of catalysts under traditional mechanisms.

Operando elucidation of hydrogen production mechanisms on sub-nanometric high-entropy metallenes

Precise morphological control and identification of structure-property relationships pose formidable challenges for high-entropy alloys, severely limiting their rational design and application in multistep and tandem reactions. Herein, we report the synthesis of sub-nanometric high-entropy metallenes with up to eight metallic elements via a one-pot wet-chemical approach. The PdRhMoFeMn high-entropy metallenes exhibit high electrocatalytic hydrogen evolution performances with 6, 23, and 26 mV overpotentials at -10 mA cm-2 in acidic, neutral, and alkaline media, respectively, and high stability. The electrochemical measurements, theoretical simulations, and operando X-ray absorption spectroscopy reveal the actual active sites along with their dynamics and synergistic mechanisms in various electrolytes. Specially, Mn sites have strong binding affinity to hydroxyl groups, which enhances the water dissociation process at Pd sites with low energy barrier while Rh sites with optimal hydrogen adsorption free energy accelerate hydride coupling, thereby markedly boosting its intrinsic ability for hydrogen production.

Hexa-atom Pt Catalyst Fabricated by a Ligand Engineering Strategy for Efficient Hydrogen Oxidation Reaction

Atomically precise supported nanocluster catalysts (APSNCs), which feature exact atomic composition, well-defined structures, and unique catalytic properties, offer an exceptional platform for understanding the structure-performance relationship at the atomic level. However, fabricating APSNCs with precisely controlled and uniform metal atom numbers, as well as maintaining a stable structure, remains a significant challenge due to uncontrollable dispersion and easy aggregation during synthetic and catalytic processes. Herein, we developed an effective ligand engineering strategy to construct a Pt6 nanocluster catalyst stabilized on oxidized carbon nanotubes (Pt6/OCNT). The structural analysis revealed that Pt6 nanoclusters in Pt6/OCNT were fully exposed and exhibited a planar structure. Furthermore, the obtained Pt6/OCNT exhibited outstanding acidic HOR performances with a high mass activity of 18.37 A ⋅ mgpt -1 along with excellent stability during a 24 h constant operation and good CO tolerance, surpassing those of the commercial Pt/C. Density functional theory (DFT) calculations demonstrated that the unique geometric and electronic structures of Pt6 nanoclusters on OCNT altered the hydrogen adsorption energies on catalytic sites and thus lowered the HOR theoretical overpotential. This work presents a new prospect for designing and synthesizing advanced APSNCs for efficient energy electrocatalysis.

Compressive strain in Cu catalysts: Enhancing generation of C2+ products in electrochemical CO2 reduction

Elastic strain in Cu catalysts enhances their selectivity for the electrochemical CO2 reduction reaction (eCO2RR), particularly toward the formation of multicarbon (C2+) products. However, the reasons for this selectivity and the effect of catalyst precursors have not yet been clarified. Hence, we employed a redox strategy to induce strain on the surface of Cu nanocrystals. Oxidative transformation was employed to convert Cu nanocrystals to CuxO nanocrystals; these were subsequently electrochemically reduced to form Cu catalysts, while maintaining their compressive strain. Using a flow cell configuration, a current density of 1 A/cm2 and Faradaic efficiency exceeding 80% were realized for the C2+ products. The selectivity ratio of C2+/C1 was also remarkable at 9.9, surpassing that observed for the Cu catalyst under tensile strain by approximately 7.6 times. In-situ Raman and infrared spectroscopy revealed a decrease in the coverage of K+ ion-hydrated water (K·H2O) on the compressively strained Cu catalysts, consistent with molecular dynamics simulations and density functional theory calculations. Finite element method simulations confirmed that reducing the coverage of coordinated K·H2O water increased the probability of intermediate reactants interacting with the surface, thereby promoting efficient C-C coupling and enhancing the yield of C2+ products. These findings provide valuable insights into targeted design strategies for Cu catalysts used in the eCO2RR.

Unconventional hcp/fcc Nickel Heteronanocrystal with Asymmetric Convex Sites Boosts Hydrogen Oxidation

Developing non-platinum group metal catalysts for the sluggish hydrogen oxidation reaction (HOR) is critical for alkaline fuel cells. To date, Ni-based materials are the most promising candidates but still suffer from insufficient performance. Herein, we report an unconventional hcp/fcc Ni (u-hcp/fcc Ni) heteronanocrystal with multiple epitaxial hcp/fcc heterointerfaces and coherent twin boundaries, generating rugged surfaces with plenty of asymmetric convex sites. Systematic analyses discover that such convex sites enable the adsorption of *H in unusual bridge positions with weakened binding energy, circumventing the over-strong *H adsorption on traditional hollow positions, and simultaneously stabilizing interfacial *H2O. It thus synergistically optimizes the HOR thermodynamic process as well as reduces the kinetic barrier of the rate-determining Volmer step. Consequently, the developed u-hcp/fcc Ni exhibits the top-rank alkaline HOR activity with a mass activity of 40.6 mA mgNi -1 (6.3 times higher than fcc Ni control) together with superior stability and high CO-tolerance. These results provide a paradigm for designing high-performance catalysts by shifting the adsorption state of intermediates through configuring surface sites.

Site-Selective Growth of fcc-2H-fcc Copper on Unconventional Phase Metal Nanomaterials for Highly Efficient Tandem CO2 Electroreduction

Copper (Cu) nanomaterials are a unique kind of electrocatalysts for high-value multi-carbon production in carbon dioxide reduction reaction (CO2RR), which holds enormous potential in attaining carbon neutrality. However, phase engineering of Cu nanomaterials remains challenging, especially for the construction of unconventional phase Cu-based asymmetric heteronanostructures. Here the site-selective growth of Cu on unusual phase gold (Au) nanorods, obtaining three kinds of heterophase fcc-2H-fcc Au-Cu heteronanostructures is reported. Significantly, the resultant fcc-2H-fcc Au-Cu Janus nanostructures (JNSs) break the symmetric growth mode of Cu on Au. In electrocatalytic CO2RR, the fcc-2H-fcc Au-Cu JNSs exhibit excellent performance in both H-type and flow cells, with Faradaic efficiencies of 55.5% and 84.3% for ethylene and multi-carbon products, respectively. In situ characterizations and theoretical calculations reveal the co-exposure of 2H-Au and 2H-Cu domains in Au-Cu JNSs diversifies the CO* adsorption configurations and promotes the CO* spillover and subsequent C-C coupling toward ethylene generation with reduced energy barriers.

Locally Varying Surface Binding Affinity on Pd-Au Nanocrystals Enhances Electrochemical Ethanol Oxidation Activity

Noble metal nanocrystals face challenges in effectively catalyzing electrochemical ethanol oxidation reaction (EOR)-represented multistep, multielectron transfer processes due to the linear scaling relationship among binding energies of intermediates, impeding independent optimization of individual elemental steps. Herein, we develop noble metal nanocrystals with a range of local surface binding affinities in close proximity to overcome this challenge. Experimentally, this is demonstrated by applying tensile strain to a Pd surface and decorating it with discrete Au atoms, forming a diversity of binding sites with varying affinities in close proximity for guest molecules, as evidenced by CO probing and density functional theory calculations. Such a surface enables reaction intermediates to migrate between different binding sites as needed for each elemental step, thereby reducing the energy barrier for the overall EOR when compared to reactions at a single site. On these tailored surfaces, we attain specific and mass activities of 32.7 mA cm-2 and 47.8 A mgPd-1 in EOR, surpassing commercial Pd/C by 10.9 and 43.8 times, respectively, and outperforming state-of-the-art Pd-based catalysts. These results highlight the promise of this approach in improving a variety of multistep, multielectron transfer reactions, which are crucial for energy conversion applications.

Controlled Synthesis of Unconventional Phase Alloy Nanobranches for Highly Selective Electrocatalytic Nitrite Reduction to Ammonia

The controlled synthesis of metal nanomaterials with unconventional phases is of significant importance to develop high-performance catalysts for various applications. However, it remains challenging to modulate the atomic arrangements of metal nanomaterials, especially the alloy nanostructures that involve different metals with distinct redox potentials. Here we report the general one-pot synthesis of IrNi, IrRhNi and IrFeNi alloy nanobranches with unconventional hexagonal close-packed (hcp) phase. Notably, the as-synthesized hcp IrNi nanobranches demonstrate excellent catalytic performance towards electrochemical nitrite reduction reaction (NO2RR), with superior NH3 Faradaic efficiency and yield rate of 98.2 % and 34.6 mg h-1 mgcat -1 (75.5 mg h-1 mgIr -1) at 0 and -0.1 V (vs reversible hydrogen electrode), respectively. Ex/in situ characterizations and theoretical calculations reveal that the Ir-Ni interactions within hcp IrNi alloy improve electron transfer to benefit both nitrite activation and active hydrogen generation, leading to a stronger reaction trend of NO2RR by greatly reducing energy barriers of rate-determining step.

Synergetic Catalytic Effect between Ni and Co in Bimetallic Phosphide Boosting Hydrogen Evolution Reaction

The application of electrochemical hydrogen evolution reaction (HER) for renewable energy conversion contributes to the ultimate goal of a zero-carbon emission society. Metal phosphides have been considered as promising HER catalysts in the alkaline environment, which, unfortunately, is still limited owing to the weak adsorption of H* and easy dissolution during operation. Herein, a bimetallic NiCoP-2/NF phosphide is constructed on nickel foam (NF), requiring rather low overpotentials of 150 mV and 169 mV to meet the current densities of 500 and 1000 mA cm-2, respectively, and able to operate stably for 100 h without detectable activity decay. The excellent HER performance is obtained thanks to the synergetic catalytic effect between Ni and Co, among which Ni is introduced to enhance the intrinsic activity and Co increases the electrochemically active area. Meanwhile, the protection of the externally generated amorphous phosphorus oxide layer improves the stability of NiCoP/NF. An electrolyser using NiCoP-2/NF as both cathode and anode catalysts in an alkaline solution can produce hydrogen with low electric consumption (overpotential of 270 mV at 500 mA cm-2).

Platinum Nanoparticles Bonded with Carbon Nanotubes for High-Performance Ampere-Level All-Water Splitting

Platinum nanoparticles loaded on a nitrogen-doped carbon nanotubes exhibit a brilliant hydrogen evolution reaction (HER) in an alkaline solution, but their bifunctional hydrogen and oxygen evolution reaction (OER) has not been reported due to the lack of a strong Pt-C bond. In this work, platinum nanoparticles bonded in carbon nanotubes (Pt-NPs-bonded@CNT) with strong Pt-C bonds are designed toward ultralow overpotential water splitting ability in alkaline solution. Benefit from the strong interaction between platinum and high conductivity carbon nanotube substrates through the Pt-C bond also the platinum nanoparticles bonded in carbon nanotube can provide more stable active sites, as a result, the Pt-NPs-bonded@CNT exhibits excellent hydrogen evolution in acid and alkaline solution with ultralow overpotential of 0.19 and 0.23 V to reach 1000 mA cm-2, respectively. Besides, it shows superior oxygen evolution electrocatalysis in alkaline solution with a low overpotential of 1.69 V at 1000 mA cm-2. Furthermore, it also exhibits high stability over 110 h against the evolution of oxygen and hydrogen at 1000 mA cm-2. This strategy paves the way to the high performance of bifunctional electrocatalytic reaction with extraordinary stability originating from optimized electron density of metal active sites due to strong metal-substrate interaction.

Galvanic replacement-induced preparation of bloom-like Pt23Ni77 for methanol coupled efficient hydrogen production

Galvanic replacement reaction (GRR) leverages the difference in metal reduction potentials to regulate the structure of nanomaterials. The crucial aspect of constructing highly active catalysts lies in the precise manipulation of both the oxidative dissolution of sacrificial template metals and reductive deposition of alternate metals. Herein, we investigated the morphological transformation of metal Ni as a sacrificial template in the presence of different amounts of H2PtCl6 solution and the Pt4+ substitution of Ni to achieve the redistribution of elements on the catalyst surface, which provides superior performance in both the methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER). The uniform distribution of Pt on a three-dimensional transition metal Ni substrate allows for the complete exposure of the noble metal to the catalyst surface. This distribution increases the reaction area, facilitating easy access for reactants and promoting electron transfer. Meanwhile, Pt (1.39 Å) has a larger atomic radius compared to Ni (1.24 Å), and the substitution reaction in the transition metal phase induces strong compressive strain, which effectively regulates the electronic structure of Ni.

Grain Boundary Tailors the Local Chemical Environment on Iridium Surface for Alkaline Electrocatalytic Hydrogen Evolution

Even though grain boundaries (GBs) have been previously employed to increase the number of active catalytic sites or tune the binding energies of reaction intermediates for promoting electrocatalytic reactions, the effect of GBs on the tailoring of the local chemical environment on the catalyst surface has not been clarified thus far. In this study, a GBs-enriched iridium (GB-Ir) was synthesized and examined for the alkaline hydrogen evolution reaction (HER). Operando Raman spectroscopy and density functional theory (DFT) calculations revealed that a local acid-like environment with H3 O+ intermediates was created in the GBs region owing to the electron-enriched surface Ir atoms at the GBs. The H3 O+ intermediates lowered the energy barrier for water dissociation and provided enough hydrogen proton to promote the generation of hydrogen spillover from the sites at the GBs to the sites away from the GBs, thus synergistically enhancing the hydrogen evolution activity. Notably, the GB-Ir catalyst exhibited a high alkaline HER activity (10 mV @ 10 mA cm-2 , 20 mV dec-1 ). We believe that our findings will promote further research on GBs and the surface science of electrochemical reactions.

Core-Shell Design of Metastable Phase Catalyst Enables Highly-Performance Selective Hydrogenation

Highly selective semihydrogenation of alkynes to alkenes is a highly important reaction for catalytic industry. Developing non-noble metal based catalysts with platinum group metal-like activity and selectivity is extremely crucial yet challenging. Metastable phase catalysts provide a potential candidate to realize high activity, yet the control of selectivity remains an open question. Here, this work first reports a metastable phase core-shell: face-centered cubic (fcc) phase Ag (10 at%) core-metastable hexagonal closest packed (hcp) phase Ni (90 at%) shell catalyst, which represents high conversion rate, high selectivity, and remarkable universality for the semihydrogenation of phenylacetylene and its derivatives. More impressively, a turnover frequency (TOF) value of 8241.8 h-1 is achieved, much higher than those of stable phase catalysts and reported platinum group metal based catalysts. Mechanistic investigation reveals that the surface of hcp Ni becomes more oxidized due to electron transfer from hcp Ni shell to fcc Ag core, which decreases the adsorption capacity of styrene on the metastable phase Ni surface, thus preventing full hydrogenation. This work has gained crucial research significance for the design of high performance metastable phase catalysts.

Preventing the Galvanic Replacement Reaction toward Unconventional Bimetallic Core-Shell Nanostructures

A bimetallic core-shell nanostructure is a versatile platform for achieving intriguing optical and catalytic properties. For a long time, this core-shell nanostructure has been limited to ones with noble metal cores. Otherwise, a galvanic replacement reaction easily occurs, leading to hollow nanostructures or completely disintegrated ones. In the past few years, great efforts have been devoted to preventing the galvanic replacement reaction, thus creating an unconventional class of core-shell nanostructures, each containing a less-stable-metal core and a noble metal shell. These new nanostructures have been demonstrated to show unique optical and catalytic properties. In this work, we first briefly summarize the strategies for synthesizing this type of unconventional core-shell nanostructures, such as the delicately designed thermodynamic control and kinetic control methods. Then, we discuss the effects of the core-shell nanostructure on the stabilization of the core nanocrystals and the emerging optical and catalytic properties. The use of the nanostructure for creating hollow/porous nanostructures is also discussed. At the end of this review, we discuss the remaining challenges associated with this unique core-shell nanostructure and provide our perspectives on the future development of the field.

Pd@PtRuNi core-shell nanowires as oxygen reduction electrocatalysts

Fuel cells, as the alternative to fossil energy, have engaged widespread attention by reason of the high conversion efficiency from the chemical energy to the electric energy combined with low pollution emissions. The cathodic ORR catalysts with excellent performance and cost-effectiveness are the dominant point towards the massive development of fuel cells. Here, our group select the Pd NWs as the template and construct the Pd@PtRuNi core-shell bilayer nanostructure to expand platinum atom utilization. Pd@PtRuNi bilayer core-shell NWs unfold elevated mass activity of1.62Amgmetal-1at 0.9 V versus RHE in alkaline media, 2.03- and 6.23-fold of pristine Pd NWs and benchmark commercial Pt/C, respectively. Meanwhile, the cyclic stability tests reveal the excellent durability of Pd@PtRuNi NWs, whose mass activity is only 13.58% degradation after accelerated durability tests. The catalytic activity and durability towards ORR are better than the U.S. 2025 DOE target (0.44Amgpt-1and less than 40% activity attenuation at 0.9 V after 30 000 potential cycles). The elevated catalytic properties can be traceable to the synergism between the ligand effect of Ni and Ru and one-dimensional structure superiority, which optimizes the electronic structure of active sites, promotes the charge transfer and restrains the agglomeration and detachment.