Substantial Impact of Built-in Electric Field and Electrode Potential on the Alkaline Hydrogen Evolution Reaction of Ru-CoP Urchin Arrays.

Although great efforts on the delicate construction of a built-in electric field (BIEF) to modify the electronic properties of active sites have been conducted, the substantial impact of BIEF coupled with electrode potential on the electrochemical reactions has not been clearly investigated. Herein, we designed an alkaline hydrogen evolution reaction (HER) catalyst composed of heterogeneous Ru-CoP urchin arrays on carbon cloth (Ru-CoP/CC) with a strong BIEF with the guidance of density functional theory (DFT) calculations. Impressively, despite its unsatisfactory activity at 10 mA cm-2 (overpotential of 44 mV), Ru-CoP/CC exhibited better activity (357 mV) than the benchmark Pt/C catalyst (505 mV) at 1 A cm-2 . Experimental and theoretical studies revealed that strong hydrogen adsorption on the interfacial Ru atoms created a high energy barrier for hydrogen desorption and spillover, resulting in unsatisfactory activity at low current densities. However, as the electrode potential became more negative (i.e., the current density increased), the barrier for hydrogen spillover from the interfacial Ru to the Co site, which had near-zero hydrogen adsorption energy, significantly decreased, thus greatly accelerating the whole alkaline HER process. This explains why the activity of Ru-CoP is relatively susceptible to the electrode potential compared to Pt/C.

Unraveling the Function of Metal-Amorphous Support Interactions in Single-Atom Electrocatalytic Hydrogen Evolution.

Amorphization of the support in single-atom catalysts is a less researched concept for promoting catalytic kinetics through modulating the metal-support interaction (MSI). We modeled single-atom ruthenium (RuSAs ) supported on amorphous cobalt/nickel (oxy)hydroxide (Ru-a-CoNi) to explore the favorable MSI between RuSAs and the amorphous skeleton for the alkaline hydrogen evolution reaction (HER). Differing from the usual crystal counterpart (Ru-c-CoNi), the electrons on RuSAs are facilitated to exchange among local configurations (Ru-O-Co/Ni) of Ru-a-CoNi since the flexibly amorphous configuration induces the possible d-d electron transfer and medium-to-long range p-π orbital coupling, further intensifying the MSI. This embodies Ru-a-CoNi with enhanced water dissociation, alleviated oxophilicity, and rapid hydrogen migration, which results in superior durability and HER activity of Ru-a-CoNi, wherein only 15 mV can deliver 10 mA cm-2 , significantly lower than the 58 mV required by Ru-c-CoNi.

Development of a highly active FeNC catalyst with the preferential formation of atomic iron sites for oxygen reduction in alkaline and acidic electrolytes.

Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesizedviacomplicated routes involving multiple heat-treatment steps to form the desired Fe-Nx sites. We herein developed a highly active FeNC catalyst comprising of exclusive Fe-Nx sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-Nx centers, which yielded a high density of electrochemically accessible active sites (1.36 × 1019 sites g-1) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E1/2) of 0.905 VRHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E1/2 of 0.760 VRHE is achieved at a low loading level (0.29 mg cm-2). In PEMFC tests, a current density of 2.3 mA cm-2 is achieved at 0.90 ViR-free under H2-O2 conditions, reflecting high kinetic activity of the optimized catalyst.

Promotion of oxygen reduction by a bio-inspired tethered iron phthalocyanine carbon nanotube-based catalyst.

Electrocatalysts for oxygen reduction are a critical component that may dramatically enhance the performance of fuel cells and metal-air batteries, which may provide the power for future electric vehicles. Here we report a novel bio-inspired composite electrocatalyst, iron phthalocyanine with an axial ligand anchored on single-walled carbon nanotubes, demonstrating higher electrocatalytic activity for oxygen reduction than the state-of-the-art Pt/C catalyst as well as exceptional durability during cycling in alkaline media. Theoretical calculations suggest that the rehybridization of Fe 3d orbitals with the ligand orbitals coordinated from the axial direction results in a significant change in electronic and geometric structure, which greatly increases the rate of oxygen reduction reaction. Our results demonstrate a new strategy to rationally design inexpensive and durable electrochemical oxygen reduction catalysts for metal-air batteries and fuel cells.

Effects of pH and dissolved oxygen on Cr(VI) removal in Fe(0)/H2O systems.

The effects of pH and dissolved oxygen (DO) on aqueous Cr(VI) removal by micro-scale zero-valent iron (Fe(0)/H(2)O system) were investigated. Batch experiments were conducted at pH 4.0, 5.0 and 6.0 under oxic and anoxic conditions. Column experiments were performed at pH 5.0 and 7.5 under oxic condition. Spectroscopic analyses were applied to explain the mechanism of Cr(VI) removal using X-ray absorption near-edge structure (XANES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results showed that the kinetics of Cr(VI) removal were fastest at pH 5 under both oxic and anoxic conditions. As a rule, Cr(VI) removal were faster under oxic conditions than under anoxic conditions. Column experiments showed that Cr(VI) removal was about 1.7-fold higher at pH 5 than at pH 7.5. XANES (X-ray absorption near edge structures) results showed that Fe(0) reduced Cr(VI) to Cr(III) under both oxic and anoxic conditions. X-ray diffraction patterns of the Cr(VI)-Fe(0) reaction products suggested partial formation of chromite (FeCr(2)O(4)) at pH 5 and 6 under oxic conditions. However, nano-sized clusters of Cr(III)/Fe(III) hydroxide/oxyhydroxide were formed on the surface of Fe(0) under anoxic conditions. These results indicate that the presence of oxygen in solution plays an important role in control of the kinetic of Cr(VI) removal and in development of various Cr(VI) reduction products.