Electrochemical hydrogen peroxide (H 2 O 2 ) production by two-electron oxygen reduction is a promising alternative process to the established industrial anthraquinone process. Current challenges relate to finding cost-effective electrocatalysts with high electrocatalytic activity, stability, and product selectivity. Here, we explore the electrocatalytic activity and selectivity toward H 2 O 2 production of a number of distinct nitrogen-doped mesoporous carbon catalysts and report a previously unachieved H 2 O 2 selectivity of ∼95−98% in acidic solution. To explain our observations, we correlate their structural, compositional, and other physicochemical properties with their electrocatalytic performance and uncover a close correlation between the H 2 O 2 product yield and the surface area and interfacial zeta potential. Nitrogen doping was found to sharply boost H 2 O 2 activity and selectivity. Chronoamperometric H 2 O 2 electrolysis confirms the exceptionally high H 2 O 2 production rate and large H 2 O 2 faradaic selectivity for the optimal nitrogen-doped CMK-3 sample in acidic, neutral, and alkaline solutions. In alkaline solution, the catalytic H 2 O 2 yield increases further, where the production rate of the HO 2 − anion reaches a value as high as 561.7 mmol g catalyst −1 h −1 with H 2 O 2 faradaic selectivity above 70%. Our work provides a guide for the design, synthesis, and mechanistic investigation of advanced carbon-based electrocatalysts for H 2 O 2 production.

We report on a non-precious, two-phase bifunctional oxygen reduction and evolution (ORR and OER) electrocatalyst with previously unachieved combined roundtrip catalytic reactivity and stability for use in oxygen electrodes of unitized reversible fuel cell/electrolyzers or rechargeable metal-air batteries. The combined OER and ORR overpotential, total, at 10 mA cm À2 was a record low value of 0.747 V. Rotating Ring Disk Electrode (RRDE) measurements revealed a high faradaic selectivity for the 4 electron pathways, while subsequent continuous MEA tests in reversible electrolyzer cells confirmed the excellent catalyst reactivity rivaling the state-of-the-art combination of iridium (OER) and platinum (ORR).Electrochemical energy storage based on the interconversion of renewable electricity and molecular fuels (solar fuels) and solid state structures (aqueous metal-air cells) invariably involves the oxygen/water redox system supplying and consuming water, protons, electrons and oxygen. This is why efficient catalysts for the oxygen evolution reaction (OER:are critical. [1][2][3][4] Combining the two functionalities in one single bifunctional oxygen redox electrode would greatly simplify the design of energy conversion devices or enhance the mobility and power-to-weight ratio. This plays an important role in spacecraft, aircraft, and ground transportation applications. Active oxygen redox catalysts such as IrO 2 or Pt are rare and expensive, which is why the development of efficient non-precious oxygen catalysts is of interest. 5-10 The layered double hydroxide of Ni and Fe (''NiFe-LDH'') is known to be one of the most active non-noble OER catalysts in alkaline solution. 5,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] In contrast, nitrogendoped carbon materials are promising non-precious candidates for the ORR. [27][28][29][30] Rather than exploring suitable bifunctional catalytic surface sites, or designing two distinct active sites on the same substrate, we propose the facile heterogeneous mixing of either material to obtain a two-phase bifunctional catalyst. This was shown for noble metal catalysts of iridium and platinum. 31,32 Recently, non-precious metal mixtures of Mn-Co oxides and carbon nanotubes have been tested. 33 Realizing that a twocomponent surface is necessary for highly active bifunctional catalysts, 34,35 in this contribution, we designed two-component NiFe-LDH -Fe-N-C catalysts resulting in today's most efficient bifunctional oxygen electrodes in 0.1 M KOH. A mutual improving effect between the two components in the two-phase structure with distinct neighbouring active sites appears key to the observed performance. Using a fast microwave-assisted solvothermal one-pot synthesis route (Fig. S1, ESI †), we prepared a carbon-supported crystalline NiFe-LDH catalyst material in a Ni/Fe ratio of B3.6 (Ni 0.78 Fe 0.22 (OH) x ) and a metal loading of B37 wt%.The X-ray diffraction (XRD) pattern (Fig. 1) is consistent with the data-based reflections of layered double hydroxides (JCPDS: 00-01...

Decades of catalysis research have created vast amounts of experimental data. Within these data, new insights into property-performance correlations are hidden. However, the incomplete nature and undefined structure of the data has so far prevented comprehensive knowledge extraction. We propose a meta-analysis method that identifies correlations between a catalyst’s physico-chemical properties and its performance in a particular reaction. The method unites literature data with textbook knowledge and statistical tools. Starting from a researcher’s chemical intuition, a hypothesis is formulated and tested against the data for statistical significance. Iterative hypothesis refinement yields simple, robust and interpretable chemical models. The derived insights can guide new fundamental research and the discovery of improved catalysts. We demonstrate and validate the method for the oxidative coupling of methane (OCM). The final model indicates that only well-performing catalysts provide under reaction conditions two independent functionalities, i.e. a thermodynamically stable carbonate and a thermally stable oxide support.

Iron can form numerous oxides, hydroxides, and oxide−hydroxides. Despite their relevance, many of the transformation processes between these phases are still poorly understood. In particular the crystallization of quasi-amorphous hydroxides and oxide−hydroxides is difficult to assess, since typical diffraction and scattering methods provide only sample-averaged information about the crystallized phases. We report a new approach for the investigation of the crystallization of oxide−hydroxides. The approach relies on model-type films that comprise a defined homogeneous nanostructure. The nanostructure allows quantitative linking of information obtained by bulk-averaging diffraction techniques (XRD, SAXS) with locally resolved information, i.e., domain sizes (SEM, TEM, LEEM) and phase composition (SAED). Using time-resolved imaging and diffraction we deduce mechanism and kinetics for the crystallization of ferrihydrite into hematite. Hematite forms via nucleation of hematite domains and subsequent domain growth that terminates only upon complete transformation. A Johnson–Mehl–Avrami–Kolmogorov model describes the kinetics over a wide temperature range. The derived understanding enables the first synthesis of ferrihydrite films with ordered mesoporosity and quantitative control over the films’ hematite and ferrihydrite content

The efficient generation of hydrogen via water electrolysis requires highly active oxygen evolution catalysts. Among the active metals, iridium oxide provides the best compromise in terms of activity and stability. The limited availability and usage in other applications demands an efficient utilization of this precious metal. Forming mixed oxides with titania promises improved Ir utilization, but often at the cost of a low catalyst surface area. Moreover, the role of Ir in establishing a sufficiently conductive mixed oxide has not been elucidated so far. We report a new approach for the synthesis of Ir/TiO mixed-oxide catalysts with defined template-controlled mesoporous structure, low crystallinity, and superior oxygen evolution reaction (OER) activity. The highly accessible pore system provides excellent Ir dispersion and avoids transport limitations. A controlled variation of the oxides Ir content reveals the importance of the catalysts electrical conductivity: at least 0.1 S m are required to avoid limitations owing to slow electron transport. For sufficiently conductive oxides a clear linear correlation between Ir surface sites and OER currents can be established, where all accessible Ir sites equally contribute to the reaction. The optimized catalysts outperform Ir/TiO materials reported in literature by about a factor of at least four.