Dispersing metals to the ultrasmall forms is an effective strategy to increase their usage efficiency and catalytic reactivity. [3,4] Recently, atomic dispersion of metal atoms has been realized over the support to form single-atom catalysts (SACs), [4-8] which attract considerable attention due to their maximized metal usage and improved active site homogeneity. [9,10] Because of the high surface energy, single metal atoms are generally formed with the existence of particles or clusters as the byproducts, prohibiting stable atomic dispersion. [11-14] As a result, it is of great importance to find efficient technologies for increasing atomic dispersion while maintaining high stability and catalytic activity during applications. Typically, two strategies are used to disperse SACs stably. One is the bottom-up method, which conventionally refers to single atoms derived from metal ions. Metal ions are captured in electronic and/or structural defects [15-17] of solid matrix such as metal oxide, [18-22] metal carbides, [23,24] zeolites/metal-organic Atomically dispersed catalysts, with maximized atom utilization of expensive metal components and relatively stable ligand structures, offer high reactivity and selectivity. However, the formation of atomic-scale metals without aggregation remains a formidable challenge due to thermodynamic stabilization driving forces. Here, a top-down process is presented that starts from iron nanoparticles, using dual-metal interbonds (RhFe bonding) as a chemical facilitator to spontaneously convert Fe nanoparticles to single atoms at low temperatures. The presence of RhFe bonding between adjacent Fe and Rh single atoms contributes to the thermodynamic stability, which facilitates the stripping of a single Fe atom from the Fe nanoparticles, leading to the stabilized single atom. The dual single-atom Rh-Fe catalyst renders excellent electrocatalytic performance for the hydrogen evolution reaction in an acidic electrolyte. This discovery of dual-metal interbonding as a chemical facilitator paves a novel route for atomic dispersion of chemical metals and the design of efficient catalysts at the atomic scale. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adma.202003484. Heterogeneous catalysis is pivotal to the modern chemical industry, [1] with many heterogeneous catalysts comprising transition or noble metals deposited over a solid support phase. [2]

Anaerobic digestion (AD) with hydrothermal (HT) pretreatment is an emerging technology for enhanced resource recovery from sewage sludge. This study investigates the speciation of Fe, P, and S during sequential HT–AD treatment of sewage sludge using sequential chemical extraction, X-ray diffraction, and X-ray absorption spectroscopy. Results suggest strong correlations between Fe and P species as well as Fe and S species, affecting the solubility and bioavailability of each other. For instance, much vivianite formed in the hydrochars after HT treatment at low temperature, while more strengite precipitated at higher HT temperature. During the subsequent AD process, microbial reduction of strengite and other Fe­(III) species led to the formation of more vivianite, with concurrent P release into the solution and adsorption onto other minerals. HT pretreatment of sewage sludge had a weak effect on the sulfidation of Fe during the AD process. This work has important implications for understanding the nutrient speciation and availability in sludge-derived hydrochars and AD solids. It also provides fundamental knowledge for the selection and optimization of HT pretreatment conditions for enhanced resource recovery through sequential HT–AD process.

Direct formic acid fuel cells (DFAFCs) are promising portable energy conversion devices for supplying our off-grid energy demands. However, traditional Pt-based catalysts suffer from poor performance; consequently the precious metal loading in an actual fuel cell has to be maintained at a very high value, typically orders of magnitude higher than the acceptable level. Through a molecular self-assembly/ electro-deposition process, Pt atoms are effectively dispersed onto the surface of a nanoporous gold substrate, and the resulting nanocomposites demonstrate superior electrocatalytic performance toward formic acid electro-oxidation, which can be attributed to a nearly ideal catalyst configuration where all the Pt atoms are involved in a highly desired direct reaction path. In both half-cell electrochemical testing and actual DFAFCs, these rationally designed electrodes show over two orders of magnitude improvement in Pt efficiency, as compared with the state-of-the-art Pt/C catalyst. This design strategy allows customized development of new generation electrocatalysts for high performance energy saving technologies.

This work describes an exogenous-oxidant-free radical C–H sulfonylation using an electrochemical oxidative protocol.