Octapod-Shaped CdSe Nanocrystals Hosting Pt with High Mass Activity for the Hydrogen Evolution Reaction

Abstract

The design of efficient electrocatalysts for electrochemical water splitting with minimal amount of precious metal is crucial to attain renewable and sustainable energy conversion. Here, we report the use of a network of CdSe branched colloidal nanocrystals, made of a CdSe core and eight CdSe pods (so-called octapods), able to host on their pods Pt particles, and thus catalyzing water splitting reactions. Thanks to the octapod shape, the resulting Pt-hosting network is mechanically trapped onto carbon nanotube buckypaper, providing mechanically flexible and binder-free electrodes. We found that such hierarchical configuration maximizes the mass activity and the utilization efficiency of Pt for the hydrogen evolution reaction (HER). At a potential of -0.15 V vs. reversible hydrogen electrode, the Pt/octapod network-based electrodes display a Pt mass activity on the HER of ~166 A mg -1 and ~42 A mg -1 in acidic and alkaline media, respectively. These values correspond to turnover frequencies of ~168 s -1 and ~42 s -1 , respectively, which are in that order 14 and 21 times higher compared to commercially available Pt/C benchmarks. The strong chemical and mechanical interactions between the Pt and the octapod surface, along with pod-aided adhesion of the Pt/octapod network to the buckypaper, result in a long-term durability (>20 h) of the HER-activity in both media. These results experimentally prove that the exploitation of our network of branched nanocrystals hosting Pt particles can circumvent the durability issues of the catalysts while adopting either ultralow Pt loadings or benchmarking carbon-supported Pt nanocrystals. Our work opens up prospects for using porous networks made by branched nanocrystals as catalysts with ultralow amount of noble metals and controlled catalytic properties. nanocrystals 21,22,[23][24][25][26][27][28][29][30]34 or monolayers 31,32 are typically embedded/deposited into/onto appropriate supports, as it is done in benchmark catalysts, such as Vulcan XC-72-supported Pt nanocrystals (Pt/C). These supports are preferably high-surface area and/or electrically conductive scaffolds. 33,35,36 However, Pt nanocrystals/monolayers often suffer from instability caused by Pt dissolution or delamination during the water splitting reactions. 37,38 The preparation of single Pt atom catalysts, e.g., Pt atoms on CeO2, 39 Al2O3, 40 TiN, 41 TiC, 41,42 carbon, 43 MXenes, 22 is challenging since the single Pt atoms tend to coalesce into clusters during the catalyst synthesis and especially during the electrocatalytic processes, 44,45 quickly degrading the theoretical maximum MAPt. 46 Therefore, it is essential to isolate and immobilize Pt atoms and to strengthen the adhesion and chemical stability of the Pt nanocrystals/monolayers, to prevent the aforementioned issues. This is achievable through the Pt localization into/onto the crystal lattice of an hosting matrix/substrate through controlled chemical interactions. 22,[47][48][49][50] The structural mismatch at the Pt/support interface can be exploi...

Microwave‐Induced Structural Engineering and Pt Trapping in 6R‐TaS2 for the Hydrogen Evolution Reaction

“…These values are significantly superior to those recently reported for Pt trapped by 2D MXene, namely Mo 2 TiC 2 T x (MA Pt = 8300 A g Pt −1 at overpotential = 77 mV), [75] and similar to the one recently reported by our group on more complex systems, namely octapod-shaped CdSe nanocrystals (MA Pt ≈20 000 A g Pt −1 at overpotential = 50 mV). [76] They are also comparable to the ones achieved by more complex atomic layer-deposition-based synthesis of N-doped graphene-supported single atom/cluster Pt (MA Pt = 10 100 A g Pt −1 at overpotential = 50 mV). [77] Overall, our data support that the interaction between Pt and TaS 2 nanoflakes is effective to maximize the MA Pt toward record-high values, as discussed in the next section.…”

“…In particular, the proposed MW treatment fragments the metallic nanoflakes, which consequently evolve from a monocrystalline to a polycrystalline structure. The modification of the structural properties regulates the HER-activity of the TaS 2 nanoflakes, lowering x -Pt for single atom Pt immobilized on MXene nanosheets, [75] NGN-Pt for N-doped graphene nanosheets supported single atom and cluster Pt, [77] MoS 2 -Pt for Pt atom-doped, few-layer MoS 2 nanosheets, [78] PCM-Pt for Pt atoms in the nitrogen-containing porous carbon matrix, [79] CdSeOCP-Pt for Pt immobilized on octapodshaped CdSe, [76] TiO 2 -Pt for sub-nanometric PtO x clusters uniformly dispersed on a TiO 2 support, [80] Ni-CoPNT-Pt single Pt atoms on CoP-based nanotube arrays supported by a Ni foam, [81] CF-Pt for Pt nanoparticles on carbon foam, [82] and CFC-WO 3 -Pt for atom cluster Pt dispersed in carbon fiber cloth supported WO 3 . [83] the overpotential at a cathodic current of 10 mA cm −2 (ƞ 10 ) from 0.377 to 0.192 V. The optimized electrodes reach a MA of the TaS 2 nanoflakes (MA TaS2 ) of 100 A g −1 at an overpotential of 0.239 V, and above 1000 A g −1 at overpotentials higher than 0.38 V. The effect of our MW treatment resembles the selfoptimizing fragmentation of the 2D group-5 TMDs occurring during in situ electrochemical preconditioning of the electrodes.…”

“…Comparison between the MA Pt of our MW1‐TaS 2 ‐CV Pt and other Pt‐based catalyst reported in literature. The following nomenclature is used in the figure to refer to catalyst: Mo 2 TiC 2 T x ‐Pt for single atom Pt immobilized on M X ene nanosheets, [ 75 ] NGN‐Pt for N‐doped graphene nanosheets supported single atom and cluster Pt, [ 77 ] MoS 2 ‐Pt for Pt atom‐doped, few‐layer MoS 2 nanosheets, [ 78 ] PCM‐Pt for Pt atoms in the nitrogen‐containing porous carbon matrix, [ 79 ] CdSeOCP‐Pt for Pt immobilized on octapod‐shaped CdSe, [ 76 ] TiO 2 ‐Pt for sub‐nanometric PtO x clusters uniformly dispersed on a TiO 2 support, [ 80 ] Ni‐CoPNT‐Pt single Pt atoms on CoP‐based nanotube arrays supported by a Ni foam, [ 81 ] CF‐Pt for Pt nanoparticles on carbon foam, [ 82 ] and CFC‐WO 3 ‐Pt for atom cluster Pt dispersed in carbon fiber cloth supported WO 3 . [ 83 ]…”

Synthesis and Characterization of π-SnS Nanoparticles and Corresponding Thin Films

“…Chemically fabricated π-SnS thin film solar cell with the structure of stainless steel (SS)/π-SnS /CdS/ZnO/ZnO:Al/Ag showed η of 1.28% with a relatively higher V OC of 0.470 eV compared to the α-SnS based solar cell [ 10 ]. On the other hand, metal monochalcogenides (SiS, SiSe, SiTe, GeS, GeSe, GeTe, SnS, and SnSe) were theoretically predicted to be economical and eco-friendly hydrogen production photocatalysts [ 12 , 13 , 14 ]. The polymorph of tin sulfide, π-SnS exhibited interesting characteristics such as a high absorption coefficient of 10 −4 cm −1 in the visible region, a direct optical bandgap of 1.7 eV, and a p-type conducting nature with dark conductivity of about 10 −6 Ω −1 cm −1 [ 9 ], and had good photoconductivity response [ 10 ].…”

Graphynes: ideal supports of single atoms for electrochemical energy conversion

“…2B-D). These two values were much smaller than that of previously developed electrocatalysts, such as MoS 2 (119 mV), 107 WS 2(1Àx) P 2x (145 mV), 108 Mo 2 C (93 mV), 109 WO x S y (103 mV), 110 and Pt/CdSe (166 mV) 111 (Fig. 2E).…”