Transition metal carbides (TMCs) have demonstrated outstanding potential for utilization in a wide range of catalytic applications because of their inherent multifunctionality and tunable composition. However, the harsh conditions required to prepare these materials have limited the scope of synthetic control over their physical properties. The development of low-temperature, carburization-free routes to prepare TMCs would unlock the versatility of this class of materials, enhance our understanding of their physical properties, and enable their cost-effective production at industrial scales. Here, we report an exceptionally mild and scalable solution-phase synthesis route to phase-pure molybdenum carbide (α-MoC1–x ) nanoparticles (NPs) in a continuous flow millifluidic reactor. We exploit the thermolytic decomposition of Mo­(CO)6 in the presence of a surface-stabilizing ligand and a high boiling point solvent to yield MoC1–x NPs that are colloidally stable and resistant to bulk oxidation in air. To demonstrate the utility of this synthetic route to prepare catalytically active TMC NPs, we evaluated the thermochemical CO2 hydrogenation performance of α-MoC1–x NPs dispersed on an inert carbon support. The α-MoC1–x /C catalyst exhibited a 2-fold increase in both activity on a per-site basis and selectivity to C2+ products as compared to the bulk α-MoC1–x analogue.

We elucidate the structural evolution of CoN4 sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)‐8‐derived carbon host as an ideal model for Co2+ ion adsorption. Subsequent in situ X‐ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co−OH and Co−O species into active CoN4 sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four‐electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal‐induced compressive strain of Co−N bonds in CoN4 active sites formed at 900 °C. Further, we developed a two‐step (i.e., Co ion doping and adsorption) Co‐N‐C catalyst with increased CoN4 site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability.

The introduction of dopants plays a key role in the physical properties of semiconductors for optoelectronic applications. However, doping is generally challenging for nanocrystals (NCs), especially for two-dimensional (2D) NCs, due to the self-annealing effect and high surface energies required for dopant addition. Here, we report an efficient doping strategy for Mn-doped 2D CsPbCl3 (i.e., Mn:CsPbCl3) nanoplatelets (NPLs) through a postsynthetic solvothermal process. While the original lightly doped 2D Mn:CsPbCl3 NPLs were obtained from growth doping, higher Mn doping efficiencies were achieved through diffusion doping under pressure-mediated solvothermal conditions, resulting in enhanced Mn photoluminescence (PL). Surprisingly, a new CsMnCl3 phase with complete dopant substitution by spinodal decomposition was observed with extended solvothermal treatment, which is confirmed by powder X-ray diffraction, X-ray absorption  fine structure, and electron paramagnetic resonance. Compared with Mn:CsPbCl3 NPLs, the pure CsMnCl3 NPLs give rise to shorter Mn PL lifetime, which is consistent with the short Mn–Mn distance within CsMnCl3 NPLs. This work provides an efficient strategy for doping inside NCs as well as new insights on the dopant concentration-dependent structural and optical properties of perovskite NCs.

Carbon electrodes chemically modified with molecular active sites are potent catalysts for key energy conversion reactions. Generally, it is assumed that these molecularly modified electrodes operate by the same redox mediation mechanisms observed for soluble molecules, in which electron transfer and substrate activation occur in separate elementary steps. Here, we uncover that, depending on the solvent, carbon-bound cobalt porphyrin can carry out electrolysis by the non-mediated mechanisms of metal surfaces in which electron transfer and substrate activation are concerted. We chemically modify glassy carbon electrodes with cobalt tetraphenylporphyrin units that are anchored by flexible aliphatic linkages to form CH-CoTPP. In acetonitrile, CH-CoTPP displays a clear outer-sphere Co(II/I) process which catalyzes the H2 evolution reaction by a step-wise, redox-mediated reaction sequence. In contrast, clear surface redox waves are not observed for CH-CoTPP in aqueous media and H2 evolution proceeds via a non-mediated, concerted proton-electron transfer reaction sequence over a wide pH range. The data suggest that, in aqueous electrolyte, the CoTPP fragments reside inside the electrochemical double layer and are electrostatically coupled to the surface. This coupling allows CH-CoTPP to carry out catalysis without being pinned to the redox potential of the molecular fragment. These studies highlight that the simple adsorption of molecules can lead to reaction mechanisms typically reserved for metal surfaces, exposing new principles for the design of molecularly-modified electrodes.