A series of six exemplary cobalt-polyoxometalate (Co-POM) precatalysts have been examined to determine if they are molecular water-oxidation catalysts (WOCatalysts) or if, instead, they actually form heterogeneous, electrode-bound CoO as the true WOCatalyst under electrochemically driven water-oxidation catalysis (WOCatalysis) conditions. Specifically, WOCatalysis derived from the following six Co-POMs has been examined at pH 5.8, 8.0, and 9.0: [Co(HO)(PWO)] (CoPW), [Co(HO)(OH)(HPO)(PWO)] (CoPW), [ ββ-Co(HO)(PWO)] (CoPW), [Co(HO)PWO] (CoPW), [α-Co(HO)PWO] (α-CoPW), and [α-Co(HO)PWO] (α-CoPW). The amount of Co(II) in 500 μM solutions of each Co-POM was measured after 3 h of aging as well as from t = 0 for pH = 5.8 and 8.0 by μM sensitive Co(II)-induced P NMR line broadening and at pH = 9.0 by cathodic stripping. The amount of detectable Co(II) after 3 h for the six Co-POMs ranges from ∼0.25 to ∼90% of the total cobalt initially present in the Co-POM. For 12 out of 18 total Co-POM and different pH cases, the amount Co(II) detected after 3 h forms heterogeneous CoO able to account for ≥100% of the observed WOCatalysis activity. However, under 0.1 M NaPi, pH 5.8 conditions for CoPW and α-CoPW where ∼1.5% and 0.25% Co(II) is detectable, the measured Co(II) cannot account for the observed WOCatalysis. The implication is that these two Co-POMs are primarily molecular, Co-POM-based, WOCatalysts under electrochemically driven, pH 5.8, phosphate-buffer conditions. Even for the single most stable Co-POM, α-CoPW, CoO is still an estimated ∼76× faster WOCatalyst at pH = 5.8 and an estimated ∼740× faster WOCatalyst at pH = 8.

The metal−organic framework (MOF) H 3 [(Cu 4 Cl) 3 − (BTTri) 8 , H 3 BTTri = 1,3,5-tris( 1 H-1,2,3-triazol-5-yl)benzene] (CuBT-Tri) is a precatalyst for biomedically relevant nitric oxide (NO) release from S-nitrosoglutathione (GSNO). The questions of the number and nature of the catalytically most active, kinetically dominant sites are addressed. Also addressed is whether or not the well-defined structural geometry of MOFs (as solid-state analogues of molecular compounds) can be used to generate specific, testable hypotheses about, for example, if intrapore vs exterior surface metal sites are more catalytically active. Studies of the initial catalytic rate vs CuBTTri particle external surface area to interior volume ratio show that intrapore copper sites are inactive within the experimental error (≤1.7 × 10 −5% of the observed catalytic activity)restated, the traditional MOF intrapore metal site catalysis hypothesis is disproven for the current system. All observed catalysis occurs at exterior surface Cu sites, within the experimental error. Fourier transform infrared (FT-IR) analysis of CN − -poisoned CuBTTri reveals just two detectable Cu sites at a ca. ≥0.5% detection limit, those that bind three or one CN − ("Cu(CN) 3 " and "CuCN"), corresponding to the CN − binding expected for exterior surface, 3-coordinate (Cu surface ) and intrapore, 5-coordinate (Cu pore ) sites predicted by the idealized, metal-terminated crystal structure. Two-coordinate Cu defect sites are ruled out at the ≥0.5% FT-IR detection limit as such defect sites would have been detectable by the FT-IR studies of the CN − -poisoned catalyst. Size-selective poisoning studies of CuBTTri exterior surface sites reveal that 1.3 (±0.4)% of total copper in 0.6 ± 0.4 μm particles is active. That counting of active sites yields a normalized turnover frequency (TOF), TOF norm = (4.9 ± 1.2) × 10 − 2 mol NO (mol Cu surface ) −1 s −1 (in water, at 20 min, 25 °C, 1 mM GSNO, 30% loss of GSNO, and 1.3 ± 0.4 mol % Cu surface ) a value ∼100× higher than the TOF calculated without active site counting. Overall, Ockham's razor interpretation of the data is that exterior surface, Cu surface sites are the catalytically most active sites present at a 1.3 (±0.4)% level of total Cu.

The question is addressed of whether the cobalt polyoxometalate (Co-POM) precatalyst Co 4 V 2 W 18 O 68 10− (hereafter Co 4 V 2 W 18 ) is a stable, homogeneous water oxidation catalyst under electrochemically driven conditions and in 0.1 M pH 5.8 and 8.0 NaPi buffer as well as pH 9.0 sodium borate (NaB) buffer. This question is of considerable interest since Co 4 V 2 W 18 has been reported to be highly stable and a 200-fold faster water oxidation catalyst than its P congener Co 4 P 2 W 18 O 68 10− (hereafter Co 4 V 2 W 18 ), for reasons that were not specified. The nature of the true water oxidation catalyst with Co 4 V 2 W 18 as the starting material is of further fundamental interest because a recent report reveals that the 51 V NMR peak at ca. −507 ppm assigned by others to Co 4 V 2 W 18 and used to argue for its solution stability is, instead, correctly assigned to the highly stable cis-V 2 W 4 O 19 4− , in turn raising the question of the true stability of Co 4 V 2 W 18 under water oxidation catalysis conditions. A battery of physical methods is used to address the questions of the stability and true water oxidation catalyst with Co 4 V 2 W 18 as the precatalyst: 31 P line-broadening detection of Co(II) present in solution from leaching or as a counterion impurity; a check of those Co(II) concentration results by the second method of cathodic stripping; the O 2 yield (and, hence, Faradaic efficiency) of electrocatalytic water oxidation; electrochemical, SEM, EDX, and XPS characterization of CoO x films produced on the electrode; and multiple controls and other experiments designed to test alternative hypotheses that might explain the observed results. The collective evidence provides a compelling case that Co(II) derived from Co 4 V 2 W 18 forms a CoO x film on the electrode which, in turn, carries all the observed, electrochemically driven water-oxidation catalysis current within experimental error. A list of seven main findings is provided as a summary.

Non-precious-metal catalysts are promising alternatives for Pt-based cathode materials in low-temperature fuel cells, which is of great environmental importance. Here, we have investigated the bifunctional electrocatalytic activity toward the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) of mixed metal (FeNi; FeMn; FeCo) phthalocyanine-modified multiwalled carbon nanotubes (MWCNTs) prepared by a simple pyrolysis method. Among the bimetallic catalysts containing nitrogen derived from corresponding metal phthalocyanines, we report the excellent ORR activity of FeCoN-MWCNT and FeMnN-MWCNT catalysts with the ORR onset potential of 0.93 V and FeNiN-MWCNT catalyst for the OER having E OER = 1.58 V at 10 mA cm –2 . The surface morphology, structure, and elemental composition of the prepared catalysts were examined with scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The FeCoN-MWCNT and FeMnN-MWCNT catalysts were prepared as cathodes and tested in anion-exchange membrane fuel cells (AEMFCs). Both catalysts displayed remarkable AEMFC performance with a peak power density as high as 692 mW cm –2 for FeCoN-MWCNT.

The vanadium-containing cobalt polyoxometalate (Co-POM) Co4V2W18O68(10-) (hereafter Co4V2W18) has been reported to be a stable, homogeneous water-oxidation catalyst, one with a claimed record turnover frequency that is also reportedly 200-fold faster than its phosphorus congener, Co4P2W18O68(10-). The claimed superior water-oxidation catalysis activity of the vanadium congener, Co4V2W18, rests squarely on the reported synthesis of Co4V2W18, its purity, and its stability in both the solid-state and in solution. Attempts to repeat the preparation of Co4V2W18 by either of two literature syntheses, along with the other studies reported herein, led to the discovery of multiple, convoluted problems in the prior literature of Co4V2W18. The three most serious of those problems proved to be the prior misunderstanding of the quadrupolar (herein (51)V) NMR peak widths in complexes that also contain paramagnetic metals such as Co(II), the incorrect assignment of a -506.8 ppm (51)V NMR to Co4V2W18, and then the use of that -506.8 peak to argue for the stability of Co4V2W18 in solution. The results are reported in a somewhat historical, "story" fashion en route to elucidating and fully supporting the 11 insights and take-home messages listed in the Summary and Conclusions section.