Pd has been regarded as one of the alternatives to Pt as a promising hydrogen evolution reaction (HER) catalyst. Strategies including Pd–metal alloys (Pd–M) and Pd hydrides (PdH x ) have been proposed to boost HER performances. However, the stability issues, e.g., the dissolution in Pd–M and the hydrogen releasing in PdH x , restrict the industrial application of Pd-based HER catalysts. We here design and synthesize a stable Pd–Cu hydride (PdCu0.2H0.43) catalyst, combining the advantages of both Pd–M and PdH x structures and improving the HER durability simultaneously. The hydrogen intercalation is realized under atmospheric pressure (1.0 atm) following our synthetic approach that imparts high stability to the Pd–Cu hydride structure. The obtained PdCu0.2H0.43 catalyst exhibits a small overpotential of 28 mV at 10 mA/cm2, a low Tafel slope of 23 mV/dec, and excellent HER durability due to its appropriate hydrogen adsorption free energy and alleviated metal dissolution rate.

proton exchange membrane fuel cells (PEMFCs). [1] Several alternative noblemetal-free catalysts have been extensively developed in the past decades, [2] among which transitional metal iron and nitrogen-doped carbon (Fe-N-C) materials have been widely reported as one of the most promising candidates. [3] Advanced spectroscopic characterizations like X-ray absorption spectroscopy (XAS) and Mössbauer spectroscopy revealed that Fe single atoms coordinated by N atoms (Fe-N x ) embedded in a graphene layer serve as the main ORR-active sites, with various coordination structures such as D1 (high-spin Fe 3+ in O-FeN 4 C 12 ) and D2 (low-or medium-spin Fe 2+ in FeN 4 C 10 ) and D3 (high-spin Fe 2+ species). [4] This triggers tremendous efforts on the synthesis of Fe-N-C catalysts with exclusively contained atomically dispersed Fe active sites, [5] for instance, pyrolyzed Fe-N-C catalysts derived from Fe-doped zeolitic imidazole framework-8 (Fe-ZIF-8). [6] Despite significant advances in the performance of Fe-N-C catalysts in PEMFCs have been achieved, [7] poor operation stability/durability of Fe-N-C catalysts has become the Achilles' heel hurdling their commercial applications. [8] Pyrolyzed Fe-N-C materials have attracted considerable interest as one of the most active noble-metal-free electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Despite significant progress is made in improving their catalytic activity during past decades, the Fe-N-C catalysts still suffer from fairly poor electrochemical and storage stability, which greatly hurdles their practical application. Here, an effective strategy is developed to greatly improve their catalytic stability in PEMFCs and storage stability by virtue of previously unexplored high-temperature synthetic chemistry between 1100 and 1200 °C. Pyrolysis at this rarely adopted temperature range not only enables the elimination of less active nitrogen-doped carbon sites that generate detrimental peroxide byproduct but also regulates the coordination structure of Fe-N-C from less stable D1 (O-FeN 4 C 12 ) to a more stable D2 structure (FeN 4 C 10 ). The optimized Fe-N-C catalyst exhibits excellent stability in PEMFCs (>80% performance retention after 30 h under H 2 /O 2 condition) and no activity loss after 35 day storage while maintaining a competitive ORR activity and PEMFC performance.

The electrochemical CO 2 reduction reaction (CO 2 RR) represents a viable alternative to help close the anthropogenic carbon cycle and convert intermittent electricity from renewable energy sources to chemical energy in the form of value-added chemicals. The development of economic catalysts possessing high faradaic efficiency (FE) and mass activity (MA) toward CO 2 RR is critical in accelerating CO 2 utilization technology. Herein, an elaborate Au−Cu catalyst where an alloyed AuCu shell caps on a Cu core (Cu@AuCu) is developed and evaluated for CO 2 -to-CO electrochemical conversion. Specific roles of Cu and Au for CO 2 RR are revealed in the alloyed core−shell structure, respectively, and a compositional-dependent volcano-plot is disclosed for the Cu@AuCu catalysts toward selective CO production. As a result, the Au 2 −Cu 8 alloyed core−shell catalyst (only 17% Au content) achieves an FE CO value as high as 94% and an MA CO of 439 mA/mg Au at −0.8 V (vs RHE), superior to the values for pure Au, reflecting its high noble metal utilization efficiency.

Selective exposure of active surfaces of Pt-based electrocatalysts has been demonstrated as an effective strategy to improve Pt utilization and promote oxygen reduction reaction (ORR) activity in fuel cell application. However, challenges remain in stabilizing those active surface structures, which often suffer undesirable degradation and poor durability along with surface passivation, metal dissolution, and agglomeration of Pt-based electrocatalysts. To overcome the aforementioned obstacles, we here demonstrate the unique (100) surface configuration enabling active and stable ORR performance for bimetallic Pt 3 Co nanodendrite structures. Using elaborate microscopy and spectroscopy characterization, it is revealed that the Co atoms are preferentially segregated and oxidized at the Pt 3 Co(100) surface. In situ X-ray absorption spectroscopy (XAS) shows that such (100) surface configuration prevents the oxygen chemisorption and oxide formation on active Pt during the ORR process. Thus, the Pt 3 Co nanodendrite catalyst shows not only a high ORR mass activity of 730 mA/mg at 0.9 V vs RHE, which is 6.6-fold higher than that of the Pt/C, but also impressively high stability with 98% current retention after the acceleration degradation test in acid media for 5000 cycles, far exceeding the Pt or Pt 3 Co nanoparticles. Density functional theory (DFT) calculation also confirms the lateral and structural effects from the segregated Co and oxides on the Pt 3 Co(100) surface in reducing the catalyst oxophilicity and the free energy for the formation of an OH intermediate in the ORR.