The milling ball is the catalyst. We introduce a palladium‐catalyzed reaction inside a ball mill, which makes catalyst powders, ligands, and solvents obsolete. We present a facile and highly sustainable synthesis concept for palladium‐catalyzed C−C coupling reactions, exemplarily showcased for the Suzuki polymerization of 4‐bromo or 4‐iodophenylboronic acid giving poly(para‐phenylene). Surprisingly, we observe one of the highest degrees of polymerization (199) reported so far.

The molecular Suzuki cross-coupling reaction was conducted mechanochemically, without solvents, ligands, or catalyst powders. Utilizing one catalytically active palladium milling ball, products could be formed in quantitative yield in as little as 30 min. In contrast to previous reports, the adjustment of milling parameters led to the complete elimination of abrasion from the catalyst ball, thus enabling the first reported systematic catalyst analysis. XPS, in situ XRD, and reference experiments provided evidence that the milling ball surface was the location of the catalysis, allowing a mechanism to be proposed. The versatility of the approach was demonstrated by extending the substrate scope to deactivated and even sterically hindered aryl iodides and bromides.

Environmentally friendly halide double perovskites with improved stability are regarded as a promising alternative to lead halide perovskites. The benchmark double perovskite, Cs2AgBiBr6, shows attractive optical and electronic features, making it promising for high‐efficiency optoelectronic devices. However, the large band gap limits its further applications, especially for photovoltaics. Herein, we develop a novel crystal‐engineering strategy to significantly decrease the band gap by approximately 0.26 eV, reaching the smallest reported band gap of 1.72 eV for Cs2AgBiBr6 under ambient conditions. The band‐gap narrowing is confirmed by both absorption and photoluminescence measurements. Our first‐principles calculations indicate that enhanced Ag–Bi disorder has a large impact on the band structure and decreases the band gap, providing a possible explanation of the observed band‐gap narrowing effect. This work provides new insights for achieving lead‐free double perovskites with suitable band gaps for optoelectronic applications.

Atom-and energy-efficient synthesis of a crystalline calcium urea sulfate ([Ca(urea) 4 ]SO 4 ) cocrystal was explored using thermally controlled mechanochemical methods with calcium sulfate compounds containing various amounts of crystalline water (CaSO 4 •xH 2 O, x = 0, 0.5, 2). Small-scale (200 mg) experiments in a shaker mill were first performed, and the progress was monitored by in situ Raman spectroscopy and in situ synchrotron powder X-ray diffraction. Time-resolved spectroscopy data revealed that the presence of water in the reagents' crystalline structure was essential to the reaction and largely determined the observed reactivity of different calcium sulfate forms. Reactions at elevated temperatures were shown to proceed significantly faster on all synthetic scales, while changes in rheology caused by adding external water hindered the reaction progress. The average yield of a 21 mm horizontal twin-screw extruder experiment was ∼5.5 g/ min of extrusion (∼330 g/h). Energy consumption during the milling reactions required to achieve complete conversion ranged from 7.6 W h/g at 70 °C for a mixer mill to 3.0 W h/g at a 50 g scale and 4.0 W h/g at a 100 g scale for a planetary mill or 4.0 W h/g at both 70 °C and RT for a twin-screw extruder, showing a significant improvement in energy efficiency at large-scale production. The obtained crystalline cocrystal exhibited a significantly lower solubility in aqueous solutions, nearly 20 times lower per molar basis compared to that of urea. Furthermore, reactive nitrogen emissions in air at 90% relative humidity, measured as NH 3 , showed slow and nearly linear nitrogen loss for the cocrystal over 90 days, while the same level of emissions was achieved with urea after 1−2 weeks, showing the potential of this cocrystal material as a large-scale nitrogen-efficient fertilizer.

One of the major challenges facing the application of layered LiNiO 2 (LNO) cathode materials is the oxygen release upon electrochemical cycling. Here it is shown that tailoring the provided lithium content during synthesis process can create a disordered layered Li 1-x Ni 1+x O 2 phase at the primary particle surface. The disordered surface, which serves as a self-protective layer to alleviate the oxygen loss, possesses the same layered rhombohedral structure (R3m) as the inner core of primary particles of the Li 1-x Ni 1+x O 2 (x ≈ 0). With advanced synchrotron-based x-ray 3D imaging and spectroscopic techniques, a macroporous architecture within the agglomerates of LNO with ordered surface (LNO-OS) is revealed after only 40 cycles, concomitant with the reduction of nickel on the primary particle surface throughout the whole secondary particles. Such chemomechanical degradation accelerates the deterioration of LNO-OS cathodes. Comparably, there are only slight changes in the nickel valence state and interior architecture of LNO with a thin disordered surface layer (LNO-DS) after cycling, mainly arising from an improved robustness of the oxygen framework on the surface. More importantly, the disordered surface can suppress the detrimental H2 ⇋ H3 phase transition upon cycling compared to the ordered one.