Fuel cell vehicles, the only all-electric technology with a demonstrated >300 miles per fill travel range, use Pt as the electrode catalyst. The high price of Pt creates a major cost barrier for large-scale implementation of polymer electrolyte membrane fuel cells. Nonprecious metal catalysts (NPMCs) represent attractive low-cost alternatives. However, a significantly lower turnover frequency at the individual catalytic site renders the traditional carbon-supported NPMCs inadequate in reaching the desired performance afforded by Pt. Unconventional catalyst design aiming at maximizing the active site density at much improved mass and charge transports is essential for the next-generation NPMC. We report here a method of preparing highly efficient, nanofibrous NPMC for cathodic oxygen reduction reaction by electrospinning a polymer solution containing ferrous organometallics and zeolitic imidazolate framework followed by thermal activation. The catalyst offers a carbon nanonetwork architecture made of microporous nanofibers decorated by uniformly distributed high-density active sites. In a single-cell test, the membrane electrode containing such a catalyst delivered unprecedented volumetric activities of 3.3 A·cm −3 at 0.9 V or 450 A·cm −3 extrapolated at 0.8 V, representing the highest reported value in the literature. Improved fuel cell durability was also observed.nanofibrous | nonprecious metal catalyst | metal-organic framework | fuel cell | oxygen reduction P olymer electrolyte membrane fuel cells (PEMFCs) electrochemically convert the chemical energy of hydrogen and oxygen to electricity while producing water as a byproduct. They have significantly higher power and energy densities than the competing electrochemical devices, such as Li-ion batteries and supercapacitors, and represent the only all-electric technology with a demonstrated cruising range of over 300 miles between refueling (1). Current PEMFCs use platinum as a catalyst to promote an oxygen reduction reaction (ORR) at the cathode and a hydrogen oxidation reaction at the anode. The Pt use at the cathode is typically three to four times more than that at the anode to overcome the kinetically more sluggish ORR. Because platinum is expensive and there are limited worldwide reserves, technologies that could substantially reduce or replace its use have to be realized before widespread PEMFC commercialization. Nonprecious metal catalysts (NPMCs) represent one such technology.* Among NPMCs, transition metal (TM) and N-doped carbonaceous composites (TM/N/Cs) have demonstrated promising ORR catalytic activities in both acidic and alkaline media, whereas TM-free composites (N/Cs) showed activities primarily in an alkaline medium (2-17). The initial discovery of ORR catalytic activity by N-ligated cobalt was reported half a century ago (18). However, it was not until recently that breakthrough performances were achieved (19-23). New surface property and synthesis strategies for continuously improving catalytic activity were also identified. For example, Lef...

A facile synthesis of non-PGM ORR electrocatalysts through thermolysis of one-pot synthesized ZIF is demonstrated. The electrocatalysts exhibit excellent activity, with a maximum volumetric current density of 88.1 A cm(-3) measured at 0.8 V in PEFC tests. This approach not only makes ZIFs-based electrocatalysts easy to scale up, but also paves the way for the tailored synthesis of electrocatalysts.

TiO2, in the rutile phase with a high concentration of self-doped Ti(3+), has been synthesized via a facile, all inorganic-based, and scalable method of oxidizing TiH2 in H2O2 followed by calcinations in Ar gas. The material was shown to be photoactive in the visible-region of the electromagnetic spectrum. Powdered X-ray diffraction (PXRD), transmission electron microscopy (TEM), ultraviolet-visible-near-infrared (UV-vis-NIR), diffuse reflectance spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) methods were used to characterize the crystalline, structural, and optical properties and specific surface area of the as-synthesized Ti(3+)-doped rutile, respectively. The concentration of Ti(3+) was quantitatively studied by electron paramagnetic resonance (EPR) to be as high as one Ti(3+) per ~4300 Ti(4+). Furthermore, methylene blue (MB) solution and an industry wastewater sample were used to examine the photocatalytic activity of the Ti(3+)-doped TiO2 which was analyzed by UV-vis absorption, Fourier transform infrared spectroscopy (FT-IR), and electrospray ionization mass spectrometry (ESI-MS). In comparison to pristine anatase TiO2, our Ti(3+) self-doped rutile sample exhibited remarkably enhanced visible-light photocatalytic degradation on organic pollutants in water.

A new approach for preparing non-precious-metal electrocatalysts using a porous organic polymer (POP) as precursor is presented. Polyporphyrin, containing a high density of nitrogen-coordinated iron macrocyclic centers, was prepared by oxidative coupling to form a porous network with a very high specific surface area and narrow pore-size distribution. Upon pyrolysis, the POP was converted into a highly active electrocatalysts for the oxygen reduction reaction in an acidic electrolyte. Proton-exchange membrane fuel cells, prepared with such catalyst at the cathode, achieved very high measured volumetric and gravimetric current densities of 20.2 A cm À3 and 39.4 A g À1 at 0.8 V, respectively, and a peak power density of 730 mW cm À2 at 0.4 V.The proton-exchange membrane fuel cell (PEMFC) is among the most efficient energy conversion devices for future transportation applications. [1] The PEMFC is operated through the electrochemical hydrogen oxidation reaction (HOR) at the anode and oxygen reduction reaction (ORR) at the cathode. The ORR generally faces higher kinetic barrier than HOR and therefore requires more catalyst. [2] At present, the electrocatalysts of choice are precious metals, such as platinum supported on a carbon substrate. High costs and limited reserves of the precious metals pose a major challenge for large scale commercialization of PEMFCs. [3] Non-precious-metal catalysts (NPMCs) made of Fe and Co in carbon composites have attracted a great deal of attentions since they were discovered with promising activities towards ORR in acidic media. [4] Their activities in alkaline or neutral media were also extensively studied, although the subject is beyond the scope of the current discussion. [5] Extensive characterizations have been carried out in attempts to understand the roles of transition metals, nitrogen, and surface properties in the catalytic activity of these NPMCs. [6] The durability of these NPMCs in the protonic medium has been a major concern, although recent work by Wu et al. demonstrated a catalyst with improved stability in the PEMFC operating environment. [4l] At present, the catalytic activities of NPMCs are still significantly less than that of precious metals. To make NPMCs truly competitive, substantial improvements in two critical properties have to be accomplished: 1) a higher turnover frequency (TOF) per active site; and 2) a greater catalytic site density per unit volume. To improve TOF requires an in-depth understanding of the influences by transition metals, organic ligands, and the support on the active site. The interdependences between these factors are still under intensive investigation. [4j] To improve active site density, a NPMC precursor with densely populated metalligand sites and high surface exposure, and preferably free of inactive support, such as carbon, would be a rational starting point. For example, the volumetric current density of NPMCs prepared by impregnating transition metal salt over porous carbon appeared to have reached an upper limit, although perf...