The development of effective and inexpensive hydrogen evolution reaction (HER) electrocatalysts for future renewable energy systems is highly desired. Platinum-based materials are the most active electrocatalysts for catalyzing HER, but reducing the use of Pt is required because of the high price and scarcity of Pt. Here, we achieve pseudo-atomic-scale dispersion of Pt, i.e. individual atoms or subnanometer clusters, on the sidewalls of single-walled carbon nanotubes (SWNTs) with a simple and readily upscalable electroplating deposition method. These SWNTs activated with an ultralow amount of Pt exhibit activity similar to that of commercial Pt/C with a notably higher (∼66–333-fold) Pt loading for catalyzing the HER under the acidic conditions required in proton exchange membrane technology. These catalysts resemble pseudo-atomic-scale Pt systems which are mainly composed of a few to tens of Pt atoms dispersed on the sidewalls of the SWNTs. The Pt loading is only 0.19–0.75 atom % at the electrode surface, and characteristic peaks for Pt cyclic voltammograms are undetectable. The atomic dispersion increases the portion of the surface active-atom sites, and therefore, notably lower Pt loading is needed to attain a high catalytic activity. Density functional theory (DFT) calculations suggest higher ability for SWNTs, in comparison to graphene, as a catalyst support for immobilizing Pt atoms, thus providing an atomic dispersion. Moreover, a high HER activity for the SWNTs activated with Pt atoms, similar to that of bulk Pt, is predicted.

Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single-shell carbon-encapsulated iron nanoparticles (SCEINs) decorated on single-walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non-noble-metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low-cost aerosol chemical vapor deposition method in a one-step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications.

Mesoporous heteroatom-doped carbon-based nanomaterials are very promising as catalysts for electrochemical energy conversion and storage. We have developed a one-step catalytic chemical vapor deposition method to grow a highly graphitized graphene nanoflake (GF)−carbon nanotube (CNT) hybrid material doped simultaneously with single atoms of N, Co, and Mo (N−Co−Mo− GF/CNT). This high-surface-area material has a mesoporous structure, which facilitates oxygen mass transfer within the catalyst film, and exhibits a high electrocatalytic activity and stability in oxygen reduction and evolution reactions (ORR and OER) in alkaline media. We have shown that in this metal (M)−N−C catalyst, M (Co, Mo)−C centers are the main sites responsible for OER, while, for ORR, both M and N−C centers synergistically serve as the active sites. We systematically investigated tuning of the ORR and OER activity of the porous catalyst depending on the choice of the underlying substrate. The ORR kinetic current and OER activity for N−Co−Mo−GF/CNT were significantly enhanced when the catalyst was deposited onto a Ni substrate, resulting in an advanced electrocatalytic performance compared to the best bifunctional ORR/OER catalysts reported so far. Using a developed scanning electrochemical microscopy analysis method, we demonstrated that the higher OER reactivity on Ni was attributable to the formation of underlying catalyst/Ni interfacial sites, which are accessible due to the porous, electrolyte-permeable structure of the catalyst.

a b s t r a c tThe success of intermittent renewable energy systems relies on the development of energy storage technologies. Particularly, active and stable water splitting electrocatalysts operating in the same electrolyte are required to enhance the overall efficiency and reduce the costs. Here we report a precise and facile synthesis method to control nitrogen active sites for producing nitrogen doped multi-walled carbon nanotube (NMWNT) with high activity toward both oxygen and hydrogen evolution reactions (OER and HER). The NMWNT shows an extraordinary OER activity, superior to the most active non-metal based OER electrocatalysts. For OER, the NMWNT requires overpotentials of only 320 and 360 mV to deliver current densities of 10 and 50 mA cm À2 in 1.0 M NaOH, respectively. This metal-free electrocatalyst also exhibits a proper performance toward HER with a moderate overpotential of 340 mV to achieve a current density of 10 mA cm À2 in 0.1 M NaOH. This catalyst also shows high stability after long-time water oxidation without notable changes in the structure of the material. It is revealed that the electron-withdrawing pyridinic N moieties in the NMWNTs could serve as the active sites for OER and HER. Our findings open up new avenues for the development of metal-free electrocatalysts for full water splitting.

Among current technologies for hydrogen production as an environmentally friendly fuel, water splitting has attracted increasing attention. However, the efficiency of water electrolysis is severely limited by the large anodic overpotential and sluggish reaction rate of the oxygen evolution reaction (OER). To overcome this issue, the development of efficient electrocatalyst materials for the OER has drawn much attention. Here, we show that organometallic Ni­(II) complexes immobilized on the sidewalls of multiwalled carbon nanotubes (MWNTs) serve as highly active and stable OER electrocatalysts. This class of electrocatalyst materials is synthesized by covalent functionalization of the MWNTs with organometallic Ni bipyridine (bipy) complexes. The Ni-bipy-MWNT catalyst generates a current density of 10 mA cm–2 at overpotentials of 310 and 290 mV in 0.1 and 1 M NaOH, respectively, with a low Tafel slope of ∼35 mV dec–1, placing the material among the most active OER electrocatalysts reported so far. Different simple analysis techniques have been developed in this study to characterize such a class of electrocatalyst materials. Furthermore, density functional theory calculations have been performed to predict the stable coordination complexes of Ni before and after OER measurements.