The development of highly active and durable inexpensive electrocatalysts for hydrogen evolution reaction (HER) is still a formidable challenge. Herein, an ordered hexagonal-closed-packed (hcp)-Ru nanocrystal coated with a thin layer of N-doped carbon (hcp-Ru@NC) was fabricated through the thermal annealing of polydopamine (PDA)-coated Ru nanoparticle (RuNP@PDA). As an alternative to Pt/C catalyst, the hcp-Ru@NC nanocatalyst exhibited the small overpotential of 27.5 mV at a current density of 10 mA cm −2 , as well as long-term stability for HER in acid media. Interestingly, the HER performance of hcp-Ru is highly dependent on its crystallinity. The calculation from density functional theory (DFT) revealed that the difference in HER activity over various exposed surface causes the crystallinity-dependent property of hcp-Ru. The results provided clues to guide the design of Ru-based inexpensive HER electrocatalyst.

Electrode materials with high activity and good stability are essential for commercialization of energy conversion systems such as solid oxide fuel cells or electrolysis cells at the intermediate temperature. Modifying the existing perovskite-based electrode surface to form a heterostructure has been widely applied for the rational design of novel electrodes with high performance. Despite many successful developments in enhancing electrode performance by surface modification, some controversial results are also reported in the literature and the mechanisms are still not well understood. In this work, the mechanism of how surface modification impacts the oxygen reduction reaction (ORR) activity and stability of perovskite-based oxides was investigated. We took La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) as the thin-film model system and modified its surface with additive Pr x Ce1–x O2 layers of different thicknesses. We found a strong correlation between surface oxygen defects and the ORR activity of the heterostructure. By inducing higher oxygen vacancy concentration compared to bare LSCF, PrO2 coating is proved to greatly facilitate the rate of oxygen dissociation, thus significantly enhancing the ORR activity. Because of low oxygen vacancy density introduced by Pr0.2Ce0.8O2 and CeO2 coating, on the one hand, it does not boost the rate of ORR but successfully suppresses surface Sr segregation, leading to an enhanced durability. Our findings demonstrate the vital role of surface oxygen defects and provide important insights for the rational design of high-performance electrode materials through surface defect engineering.

The development of a highly active and exceedingly durable electrocatalyst at low cost for the oxygen reduction reaction (ORR) is extremely desirable but remains to be a grand challenge. Over the past decade, the transitional-metal (e.g., Fe, Co, Ni) and N codoped graphene materials have attracted most attention as the state-of-the-art nonprecious-metal-based effective electrocatalyst for ORR but still entail unsatisfactory issues such as moderate activity and life. Herein, the main-group-metal Al and N codoped graphene (ANG) is successfully fabricated via thermal annealing treatment of N-doped graphene with aluminum tri-(8-hydroxyquinoline). As a highly effective electrocatalyst for ORR, the as-prepared ANG exhibits not only high electrocatalytic activity that even outperforms the commercial Pt/C but also good durability in both three-electrode cell and Zn-air battery. Theoretical calculations show that the inhomogeneous charge density distribution and the interaction between Al and N are mainly responsible for the marked enhancement of ORR activity. The designed ANG electrocatalysts will provide a perspective application in energy storage and promote further exploration of main-group-element-based inexpensive, active, and durable electrocatalysts.

Commercialization of fuel cell technologies hinges on the development of solid electrolytes of sufficient ionic conductivity at intermediate temperatures (200−600 °C). Here we report a novel proton conductor derived from Li 13.9 Sr 0.1 Zn(GeO 4 ) 4 (LSZG), demonstrating the highest protonic conductivity (0.034 S cm −1 at 600 °C) among all known proton conducting ceramics, which is much higher than those of several well-known oxygen ion conducting electrolytes (e.g., ∼0.009 and 0.018 S cm −1 , respectively, for zirconia-and ceria-based oxide electrolyte at 600 °C). Interestingly, after fully replacing the mobile Li + ions by H + through proper ion exchange, the H + conductivity increases from 0.034 to 0.048 S cm −1 at 600 °C. A simple but effective ab initio molecular dynamics simulation study suggests a unique H + /Li + transport mechanism: the proton in LSZG moves freely in the Li + interstitial space within the 3D Li + transport network (i.e., 4c and 4a sites, as the occupancies of the Li1 and Li2 sites are 55% and 16%, respectively). In particular, a solid oxide fuel cell (SOFC) based on an LSZG electrolyte (∼40 μm thick) demonstrates high open circuit voltage (∼1.1 V) and good peak power density (377 mW cm −2 ) at 600 °C. The cell performance may be further improved if the electrode−electrolyte interface can be optimized. The new transport mechanism and excellent proton conductivity suggest that the LSZG represents an important family of electrolyte materials, which may be used as a proton-conducting membrane for intermediate-temperature SOFCs and hydrogen production or separation.