HCl gas hydrolysis of a bacterial cellulose (BC) aerogel followed by 2,2,6,6-tetramethylpiperidine-1-oxyl radical-mediated oxidation was used to produce hydrolyzed BC with carboxylate groups, which subsequently disintegrated into a stable dispersion of cellulose nanocrystals (CNCs). The degree of polymerization was successfully reduced from 2160 to 220 with a CNC yield of >80%.

Cellulose hydrolysis is an extensively studied process due to its relevance in the fields of biofuels, chemicals production, and renewable nanomaterials. However, the direct visualization of the process accompanied with detailed scaling has not been reported because of the vast morphological alterations occurring in cellulosic fibers in typical heterogeneous (solid/liquid) hydrolytic systems. Here, we overcome this distraction by exposing hardwood cellulose nanofibers (CNFs) deposited on silica substrates to pressurized HCl gas in a solid/gas system and examine the changes in individual CNFs by atomic force microscopy (AFM). The results revealed that hydrolysis proceeds via an intermediate semi-fibrous stage before objects reminiscent of cellulose nanocrystals were formed. The length of the nanocrystal-like objects correlated well with molar mass, as analyzed by gel permeation chromatography, performed on CNF aerogels hydrolyzed under identical conditions. Meanwhile, X-ray diffraction showed a slight increase in crystallinity index as the hydrolysis proceeded. The results provide a modern visual complement to >100 years of research in cellulose degradation.

Efficient, abundant and low‐cost catalysts for the oxygen evolution reaction (OER) are required for energy conversion and storage. In this study, a doping–etching route has been developed to access defect rich Fe–Co–Al (Fe–Co–Al‐AE) ternary hydroxide nanosheets for superior electrochemical oxygen evolution. After partial etching of Al, ultrathin Fe3Co2Al2‐AE electrocatalysts with a rich pore structure are obtained with a shift of the cobalt valence state towards higher valence (Co2+→Co3+), along with a substantial improvement in the catalytic performance. Fe3Co2Al2‐AE shows a notably lower overpotential of only 284 mV at a current density of 10 mA cm−2 and double the OER mass activity of the etching‐free Fe3Co2Al2 with an overpotential of 350 mV. Density functional theory shows the leaching of Al changes the rate‐determining step of the OER from conversion of *OOH into O2 on Fe3Co2Al2 to formation of OOH from *O on the Al‐defective catalysts. This work demonstrates an effective route to design and synthesize transition metal electrocatalysts and provides a promising alternative for the further development of oxygen evolution catalysts.