Tuning the surface strain of heterogeneous catalysts represents a powerful strategy to engineer their catalytic properties by altering the electronic structures. However, a clear and systematic understanding of strain effect in electrochemical reduction of carbon dioxide is still lacking, which restricts the use of surface strain as a tool to optimize the performance of electrocatalysts. Herein, we demonstrate the strain effect in electrochemical reduction of CO by using Pd octahedra and icosahedra with similar sizes as a well-defined platform. The Pd icosahedra/C catalyst shows a maximum Faradaic efficiency for CO production of 91.1 % at -0.8 V versus reversible hydrogen electrode (vs. RHE), 1.7-fold higher than the maximum Faradaic efficiency of Pd octahedra/C catalyst at -0.7 V (vs. RHE). The combination of molecular dynamic simulations and density functional theory calculations reveals that the tensile strain on the surface of icosahedra boosts the catalytic activity by shifting up the d-band center and thus strengthening the adsorption of key intermediate COOH*. This strain effect was further verified directly by the surface valence-band photoemission spectra and electrochemical analysis.

We report a facile synthesis of multiply twinned Pd@Pt core-shell concave decahedra by controlling the deposition of Pt on preformed Pd decahedral seeds. The Pt atoms are initially deposited on the vertices of a decahedral seed, followed by surface diffusion to other regions along the edges/ridges and then across the faces. Different from the coating of a Pd icosahedral seed, the Pt atoms prefer to stay at the vertices and edges/ridges of a decahedral seed even when the deposition is conducted at 200 °C, naturally generating a core-shell structure covered by concave facets. The nonuniformity in the Pt coating can be attributed to the presence of twin boundaries at the vertices, as well as the {100} facets and twin defects along the edges/ridges of a decahedron, effectively trapping the Pt adatoms at these high-energy sites. As compared to a commercial Pt/C catalyst, the Pd@Pt concave decahedra show substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). For the concave decahedra with 29.6% Pt by weight, their specific (1.66 mA/cm(2)Pt) and mass (1.60 A/mgPt) ORR activities are enhanced by 4.4 and 6.6 times relative to those of the Pt/C catalyst (0.36 mA/cm(2)Pt and 0.32 A/mgPt, respectively). After 10,000 cycles of accelerated durability test, the concave decahedra still exhibit a mass activity of 0.69 A/mgPt, more than twice that of the pristine Pt/C catalyst.

This review aims to provide comprehensive insights into how to improve the stability of Pt-based catalysts for ORR. First, the basic physical chemistry behind the catalyst degradation, including the fundamental understandings of carbon corrosion, catalyst dissolution, and particle sintering, is highlighted. After a discussion of advanced characterization techniques for the catalyst degradation, the design strategies for improving the stability of Pt-based catalysts are summarized. Finally, further insights into the remaining challenges and future research directions are also provided.

Alloying 3d transition metals with Pt has been discovered as an effective strategy to boost the catalytic activity in oxygen reduction reaction (ORR), which, however, often raises the insufficient catalyst durability issue due to rapid leaching of the 3d metal elements. To overcome this issue and realize enhancements in both the activity and the durability properties, here we report a new catalytic structure based on PtGa ultrathin alloy nanowires (NWs), which feature an unconventional strong p−d hybridization interaction. Relative to commercial Pt catalyst, the optimum Pt 4.31 Ga NWs catalyst exhibited 10.5-and 12.1-fold enhancement in the ORR mass activity and specific activity, respectively. Particularly, the Pt 4.31 Ga NWs catalyst showed only 15.8% loss in the mass activity after 30 000 cycles of durability test, as compared to a big decrease of 79.6% for the commercial Pt catalyst. Our mechanistic studies find a strong p−d hybridization interaction between Ga and Pt that accounts for the improved ORR performance via synergistically optimizing the surface electronic structure, enhancing the oxidation resistance of Pt, and suppressing the leaching of lattice Ga. We believe this work provides new perspectives to design active and durable electrocatalysts toward ORR.

The research of active and sustainable electrocatalysts toward oxygen reduction reaction (ORR) is of great importance for industrial application of fuel cells. Here, we report a remarkable ORR catalyst with both excellent mass activity and durability based on sub 2 nm thick Rh-doped Pt nanowires, which combine the merits of high utilization efficiency of Pt atoms, anisotropic one-dimensional nanostructure, and doping of Rh atoms. Compared with commercial Pt/C catalyst, the Rh-doped Pt nanowires/C catalyst shows a 7.8 and 5.4-fold enhancement in mass activity and specific activity, respectively. The combination of extended X-ray absorption fine structure analysis and density functional theory calculations reveals that the compressive strain and ligand effect in Rh-doped Pt nanowires optimize the adsorption energy of hydroxyl and in turn enhance the specific activity. Moreover, even after 10000 cycles of accelerated durability test in O condition, the Rh-doped Pt nanowires/C catalyst exhibits a drop of 9.2% in mass activity, against a big decrease of 72.3% for commercial Pt/C. The improved durability can be rationalized by the increased vacancy formation energy of Pt atoms for Rh-doped Pt nanowires.

Palladium has been recognized as the best anodic, monometallic electrocatalyst for the formic acid oxidation (FAO) reaction in a direct formic acid fuel cell. Here we report a systematic study of FAO on a variety of Pd nanocrystals, including cubes, right bipyramids, octahedra, tetrahedra, decahedra, and icosahedra. These nanocrystals were synthesized with approximately the same size, but different types of facets and twin defects on their surfaces. Our measurements indicate that the Pd nanocrystals enclosed by {1 0 0} facets have higher specific activities than those enclosed by {1 1 1} facets, in agreement with prior observations for Pd single‐crystal substrates. If comparing nanocrystals predominantly enclosed by a specific type of facet, {1 0 0} or {1 1 1}, those with twin defects displayed greatly enhanced FAO activities compared to their single‐crystal counterparts. To rationalize these experimental results, we performed periodic, self‐consistent DFT calculations on model single‐crystal substrates of Pd, representing the active sites present in the nanocrystals used in the experiments. The calculation results suggest that the enhancement of FAO activity on defect regions, represented by Pd(2 1 1) sites, compared to the activity of both Pd(1 0 0) and Pd(1 1 1) surfaces, could be attributed to an increased flux through the HCOO‐mediated pathway rather than the COOH‐mediated pathway on Pd(2 1 1). Since COOH has been identified as a precursor to CO, a site‐poisoning species, a lower coverage of CO at the defect regions will lead to a higher activity for the corresponding nanocrystal catalysts, containing those defect regions.

Closing the carbon-, hydrogen-, and nitrogen cycle with renewable electricity holds promises for the mitigation of the facing environment and energy crisis, along with the continuing prosperity of the human society. Descriptors bridge the gap between the physicochemical factors of electrocatalysts and their boosted activity and serve as guiding principles during the rational design of electrocatalysts. The optimal adsorption strength of key intermediates is potentially accessed under the tendentious guidelines proposed by indicators, such as d-band center, ΔG H , E O* , coordination number (CN), bond length, etc. Here, in this review, a comprehensive summary of the recent advances achieved regarding the descriptors during the rational design of electrocatalysts that aims for the recycling of C/H/N-containing chemicals is offered. The review is initiated by providing the necessity of the development of efficient electrocatalysts and then the physics behind the d-band center is introduced. Then a summary of the recent progress relating to the development of electrocatalysts under the guidance of descriptors is reviewed. Following that, an extended discussion regarding the experimental or theoretical characterization of the d-band center and the descriptors beyond it is provided. Finally, perspectives and challenges in this area are offered.

The extensive deployment of the electrocatalytic CO 2 reduction reaction (CO 2 RR) is presently limited by the utilization of alkaline/neutral electrolytes in which carbonate formation severely reduces the carbon efficiency and electrolysis stability. By contrast, the CO 2 RR in a strong acid electrolyte can overcome these shortcomings, yet the hydrogen evolution reaction (HER) greatly outcompetes the CO 2 RR in acidic media. Herein, CO 2 reduction to HCOOH, a significant chemical intermediate in many industrial processes, was realized in strong acid (pH ≤ 1) through introducing K + cations into the electrolyte. The K + -assisted acidic CO 2 RR accordingly manufactured HCOOH with a high Faradaic efficiency of 92.2% @−1.23 V RHE and a commercially relevant current density of −237.1 mA cm −2 . More importantly, a high single-pass carbon efficiency of 27.4% for HCOOH production was demonstrated in acid, which exceeded the value obtained in the alkaline CO 2 RR. Further mechanistic studies demonstrated that K + can engineer the local microenvironment over the Bi catalyst surface by reducing the proton coverage to suppress the competing HER and creating local interaction to stabilize the *OCOH intermediate, which ultimately promotes high-efficiency CO 2 conversion to HCOOH in strong acidic media.