Bioinspired and Bioderived Aqueous Electrocatalysis.

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO2 reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices.

Triazine-Based Graphitic Carbon Nitride Thin Film as a Homogeneous Interphase for Lithium Storage.

Triazine-based graphitic carbon nitride is a semiconductor material constituted of cross-linked triazine units, which differs from widely reported heptazine-based carbon nitrides. Its triazine-based structure gives rise to significantly different physical chemical properties from the latter. However, it is still a great challenge to experimentally synthesize this material. Here, we propose a synthesis strategy via vapor-metal interfacial condensation on a planar copper substrate to realize homogeneous growth of triazine-based graphitic carbon nitride films over large surfaces. The triazine-based motifs are clearly shown in transmission electron microscopy with high in-plane crystallinity. An AB-stacking arrangement of the layers is orientationlly parallel to the substrate surface. Eventually, the as-prepared films show dense electrochemical lithium deposition attributed to homogeneous charge transport within this thin film interphase, making it a promising solution for energy storage.

Atomic metal coordinated to nitrogen-doped carbon electrocatalysts for proton exchange membrane fuel cells: a perspective on progress, pitfalls and prospectives.

Proton exchange membrane fuel cells require reduced construction costs to improve commercial viability, which can be fueled by elimination of platinum as the O2 reduction electrocatalyst. The past 10 years has seen significant developments in synthesis, characterisation, and electrocatalytic performance of the most promising alternative electrocatalyst; single metal atoms coordinated to nitrogen-doped carbon (M-N-C). In this Perspective we recap some of the important achievements of M-N-Cs in the last decade, as well as discussing current knowledge gaps and future research directions for the community. We provide a new outlook on M-N-C stability and atomistic understanding with a set of original density functional theory simulations.

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta-Coordinated Sites.

Atomic Fe in N-doped carbon (FeNC) electrocatalysts for oxygen (O2 ) reduction at the cathode of proton exchange membrane fuel cells are the most promising alternative to platinum-group-metal catalysts. Despite recent progress on atomic FeNC O2  reduction, their controlled synthesis and stability for practical applications remain challenging. A two-step synthesis approach has recently led to significant advances in terms of Fe-loading and mass activity; however, the Fe utilization remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, this issue is addressed by coordinating Fe in a highly porous nitrogen-doped carbon support (≈3295 m2  g-1 ), prepared by pyrolysis of inexpensive 2,4,6-triaminopyrimidine and a Mg2+ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54 × 1019  sites gFeNC -1  and a record 52% FeNx electrochemical utilization based on in situ nitrite stripping are achieved. The Fe single atoms are characterized pre- and post-electrochemical accelerated stress testing by aberration-corrected high-angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X-ray absorption spectroscopy and low-temperature Mössbauer spectroscopy suggest the presence of penta-coordinated Fe sites, which are further studied by density functional theory calculations.

Metal coordination in C2N-like materials towards dual atom catalysts for oxygen reduction.

Single-atom catalysts, in particular the Fe-N-C family of materials, have emerged as a promising alternative to platinum group metals in fuel cells as catalysts for the oxygen reduction reaction. Numerous theoretical studies have suggested that dual atom catalysts can appreciably accelerate catalytic reactions; nevertheless, the synthesis of these materials is highly challenging owing to metal atom clustering and aggregation into nanoparticles during high temperature synthesis treatment. In this work, dual metal atom catalysts are prepared by controlled post synthetic metal-coordination in a C2N-like material. The configuration of the active sites was confirmed by means of X-ray adsorption spectroscopy and scanning transmission electron microscopy. During oxygen reduction, the catalyst exhibited an activity of 2.4 ± 0.3 A gcarbon -1 at 0.8 V versus a reversible hydrogen electrode in acidic media, comparable to the most active in the literature. This work provides a novel approach for the targeted synthesis of catalysts containing dual metal sites in electrocatalysis.