Cation Effects on Hydrogen Oxidation Reaction on Pt Single-Crystal Electrodes in Alkaline Media.

The exact mechanism behind the cation-assisted hydrogen oxidation reaction (HOR) on platinum electrodes in alkaline media remains disputed. We show that the cation effects at platinum display a remarkable structure sensitivity: not only the H adsorption but also the HOR activity on (111) terrace sites are independent of the nature of cation and cation concentration. On (110) step sites, at low cation concentration and mildly alkaline media, cations promote the HOR, whereas at more alkaline pH and consequently higher near-surface cation concentrations, the HOR is inhibition by the cations. Moreover, the role of the cation on terrace-OHad is different from that on step-OHad, as can also be observed from the inhibition of the HOR current by terrace-OHad at higher potentials. These results suggest that near the onset potential, HOR mainly takes place on steps, but under diffusion-limited conditions at higher overpotential, HOR mainly takes place on terraces.

Engineering the Near-Surface of PtRu3 Nanoparticles to Improve Hydrogen Oxidation Activity in Alkaline Electrolyte.

Tailoring the near-surface composition of Pt-based alloy can optimize the surface chemical properties of a nanocatalyst and further improve the sluggish H2 electrooxidation performance in an alkaline electrolyte. However, the construction of alloy nanomaterials with a precise near-surface composition and smaller particle size still needs to overcome huge obstacles. Herein, ultra-small PtRu3 binary nanoparticles (<2 nm) evenly distributed on porous carbon (PtRu3 /PC), with different near-surface atomic compositions (Pt-increased and Ru-increased), are successfully synthesized. XPS characterizations and electrochemical test confirm the transformation of a near-surface atomic composition after annealing PtRu3 /PC-300 alloy; when annealing in CO atmosphere, forming the Pt-increased near-surface structure (500 °C), while the Ru-increased near-surface structure appears in an Ar heat treatment process (700 °C). Furthermore, three PtRu3 /PC nanocatalysts all weaken the hydrogen binding strength relative to the Pt/PC. Remarkably, the Ru-increased nanocatalyst exhibits up to 38.8-fold and 9.2-fold HOR improvement in mass activity and exchange current density, compared with the Pt/PC counterpart, respectively. CO-stripping voltammetry tests demonstrate the anti-CO poisoning ability of nanocatalysts, in the sequence of Ru-increased ≥ PtRu3 /PC-300 > Pt-increased > Pt/PC. From the perspective of engineering a near-surface structure, this study may open up a new route for the development of high-efficiency electrocatalysts with a strong electronic effect and oxophilic effect.

Random alloy and intermetallic nanocatalysts in fuel cell reactions.

Fuel cells that use small organic molecules or hydrogen as the anode fuel can power clean electric vehicles. From an experimental perspective, the possible fuel cells' electrocatalytic reaction mechanisms are obtained through in situ electrochemical spectroscopy techniques and density functional theory calculations, providing theoretical guidance for further development of novel nanocatalysts. As advanced nanocatalysts for fuel cells' electrochemical reactions, alloy nanomaterials have greatly improved electrocatalytic activity and stability and have attracted widespread attention. Enhanced electrocatalytic performance of alloy nanocatalysts could be closely related to the synergistic effects, such as electronic and strain effects. Depending on the arrangement of atoms, alloys can be classified into random alloy and intermetallic compounds (ordered structure). Intermetallic compounds generally have lower heats of formation and stronger heteroatomic bonding strength relative to the random alloy, resulting in high chemical and structural stability in either full pH solutions or electrochemical tests. Here, we summarize the latest advances and the structure-function relationship of noble metal alloy nanocatalysts, among which Pt-based catalysts are the main ones, as well as comprehensively understand why they significantly affect the electrocatalytic performance of fuel cells. Novel alloy nanocatalysts with a robust three-phase interface to achieve efficient charge and mass transfer can obtain desirable activity and stability in the electrochemical workstation tests, and is expected to acquire a higher power density on fuel cell test systems with harsh test conditions.

Interfacial Structure of Water as a New Descriptor of the Hydrogen Evolution Reaction.

Driven by the persisting poor understanding of the sluggish kinetics of the hydrogen evolution reaction (HER) on Pt in alkaline media, a direct correlation of the interfacial water structure and activity is still yet to be established. Herein, using Pt and Pt-Ni nanoparticles we first demonstrate a strong dependence of the proton donor structure on the HER activity and pH. The structure of the first layer changes from the proton acceptors to the donors with increasing pH. In the base, the reactivity of the interfacial water varied its structure, and the activation energies of water dissociation increased in the sequence: the dangling O-H bonds < the trihedrally coordinated water < the tetrahedrally coordinated water. Moreover, optimizing the adsorption of H and OH intermediates can re-orientate the interfacial water molecules with their H atoms pointing towards the electrode surface, thereby enhancing the kinetics of HER. Our results clarified the dynamic role of the water structure at the electrode-electrolyte interface during HER and the design of highly efficient HER catalysts.

Facile Preparation of Carbon Shells-Coated O-Doped Molybdenum Carbide Nanoparticles as High Selective Electrocatalysts for Nitrogen Reduction Reaction under Ambient Conditions.

Electrochemical nitrogen reduction reaction (NRR) has been considered as a promising alternative to the traditional Haber-Bosch process for the preparation of ammonia (NH3) under ambient conditions. The development of cost-effective electrocatalysts with suppressive activity for hydrogen evolution reaction is critical for improving the efficiency of NRR. Herein, oxygen-containing molybdenum carbides (O-MoC) embedded in nitrogen-doped carbon layers (N-doped carbon) can be easily fabricated by pyrolyzing the chelate of dopamine and molybdate. A rate of NH3 formation of 22.5 µg·h-1·mgcat-1 is obtained at -0.35 V versus reversible hydrogen electrode with a high faradaic efficiency of 25.1% in 0.1 mM HCl + 0.5 M Li2SO4. Notably, the synthesized O-MoC@NC-800 also exhibits high selectivity (no formation of hydrazine) and electrochemical stability. The moderate electron structure induced by the interaction between O-MoC and N-doped carbon shells can effectively weaken the activity of hydrogen evolution reaction and increase the faradaic efficiency of NRR. Additionally, by applying the in situ Fourier transform infrared spectroscopy, an associative reaction pathway is proposed on O-MoC@NC-800. This work provides new insights into the rational design of carbon-encapsulated metal nanoparticles as efficient catalysts for NRR at ambient conditions.