Establishing reaction networks in the 16-electron sulfur reduction reaction

The sulfur reduction reaction (SRR) plays a central role in high-capacity lithium sulfur (Li-S) batteries. The SRR involves an intricate, 16-electron conversion process featuring multiple lithium polysulfide intermediates and reaction branches1-3. Establishing the complex reaction network is essential for rational tailoring of the SRR for improved Li-S batteries, but represents a daunting challenge4-6. Herein we systematically investigate the electrocatalytic SRR to decipher its network using the nitrogen, sulfur, dual-doped holey graphene framework as a model electrode to understand the role of electrocatalysts in acceleration of conversion kinetics. Combining cyclic voltammetry, in situ Raman spectroscopy and density functional theory calculations, we identify and directly profile the key intermediates (S8, Li2S8, Li2S6, Li2S4 and Li2S) at varying potentials and elucidate their conversion pathways. Li2S4 and Li2S6 were predominantly observed, in which Li2S4 represents the key electrochemical intermediate dictating the overall SRR kinetics. Li2S6, generated (consumed) through a comproportionation (disproportionation) reaction, does not directly participate in electrochemical reactions but significantly contributes to the polysulfide shuttling process. We found that the nitrogen, sulfur dual-doped holey graphene framework catalyst could help accelerate polysulfide conversion kinetics, leading to faster depletion of soluble lithium polysulfides at higher potential and hence mitigating the polysulfide shuttling effect and boosting output potential. These results highlight the electrocatalytic approach as a promising strategy for tackling the fundamental challenges regarding Li-S batteries

Synthesis of ultrahigh-metal-density single-atom catalysts via metal sulfide-mediated atomic trapping

Single-atom catalysts (SACs) exhibit exceptional intrinsic activity per metal site, but are often limited by low metal loading, which compromises the overall catalytic performance. Pyrolytic strategies commonly used for synthesizing SACs generally suffer from aggregation at high metal loadings. Here we report a universal synthesis approach for ultrahigh-density metal–nitrogen–carbon (UHDM–N–C) SACs via a metal-sulfide-mediated atomization process. We show that our approach is general for transition, rare-earth and noble metals, achieving 17 SACs with metal loadings >20 wt% (including a loading of 26.9 wt% for Cu, 31.2 wt% for Dy and 33.4 wt% for Pt) at 800 °C, as well as high-entropy quinary and vicenary SACs with ultrahigh metal contents. In situ X-ray diffraction and transmission electron microscopy alongside molecular simulations reveals a dynamic nanoparticle-to-single atom transformation process, including thermally driven decomposition of the metal sulfide and the trapping of liberated metal atoms to form thermodynamically stable M–N–C moieties. Our studies indicate that a high N-doping is crucial for achieving ultrahigh-loading metal atoms and a metal-sulfide-mediated process is essential for avoiding metal aggregation at high loadings. As a demonstration, the metal-loading-dependent activity in electrocatalytic oxygen evolution reaction is demonstrated on SACs with increasing Ni content. (Figure presented.

Single-atom tailoring of platinum nanocatalysts for high-performance multifunctional electrocatalysis

Platinum-based nanocatalysts play a crucial role in various electrocatalytic systems that are important for renewable, clean energy conversion, storage and utilization. However, the scarcity and high cost of Pt seriously limit the practical application of these catalysts. Decorating Pt catalysts with other transition metals offers an effective pathway to tailor their catalytic properties, but often at the sacrifice of the electrochemical active surface area (ECSA). Here we report a single-atom tailoring strategy to boost the activity of Pt nanocatalysts with minimal loss in surface active sites. By starting with PtNi alloy nanowires and using a partial electrochemical dealloying approach, we create single-nickel-atom-modified Pt nanowires with an optimum combination of specific activity and ECSA for the hydrogen evolution, methanol oxidation and ethanol oxidation reactions. The single-atom tailoring approach offers an effective strategy to optimize the activity of surface Pt atoms and enhance the mass activity for diverse reactions, opening a general pathway to the design of highly efficient and durable precious metal-based catalysts

Single-atom tailoring of platinum nanocatalysts for high-performance multifunctional electrocatalysis

Platinum-based nanocatalysts play a crucial role in various electrocatalytic systems that are important for renewable, clean energy conversion, storage and utilization. However, the scarcity and high cost of Pt seriously limit the practical application of these catalysts. Decorating Pt catalysts with other transition metals offers an effective pathway to tailor their catalytic properties, but often at the sacrifice of the electrochemical active surface area (ECSA). Here we report a single-atom tailoring strategy to boost the activity of Pt nanocatalysts with minimal loss in surface active sites. By starting with PtNi alloy nanowires and using a partial electrochemical dealloying approach, we create single-nickel-atom-modified Pt nanowires with an optimum combination of specific activity and ECSA for the hydrogen evolution, methanol oxidation and ethanol oxidation reactions. The single-atom tailoring approach offers an effective strategy to optimize the activity of surface Pt atoms and enhance the mass activity for diverse reactions, opening a general pathway to the design of highly efficient and durable precious metal-based catalysts

Surface and Interface Engineering of Platinum Nanostructures for Effective Electrochemical Energy Conversion and Storage

Electrochemical processes play a central role in clean energy generation, storage, and utilization. The rapid development of fuel cells that can efficiently convert chemical fuels to electricity will significantly reduce fossil fuel combustion to enable a sustainable future. Besides, water electrolysis is an essential environmentally friendly technique for the future hydrogen economy and vehicle market. The efficiency of these electrochemical processes relies on the rational design of high-performing electrocatalysts, which requires an atomic-level understanding of the charge/mass transfer and chemical transformation at the surface and interface of the electrocatalysts. The extent to which nanostructuring produces high performing surface and interface for efficient energy transformation is likely to cover a wide range of metal/metal alloys, transition metal oxides, sulfides, and nitrides, and is currently the focus of intensive research. To date, noble metal platinum (Pt) has been proved to be the most active element to catalyze most of the electrochemical reactions required in the fuel cells and water electrolyzers. Due to the high cost of Pt and the high energy consumption resulted from the inevitable overpotential of those electrochemical reactions, optimizing the specific activity (SA), mass activity (MA), and the overpotential presents the key challenges for the design of commercial electrochemical catalysts. This requires the systematic and controllable surface/interface engineering of the Pt catalysts for the rapid electron and mass transfer. The first part of my dissertation presents how the single-atom nickel-modified Pt nanowires (SANi-PtNWs) with abundant activated Pt sites next to the SANi and minimal blockage of the surface Pt sites can be synthesized using a partial electrochemical dealloying approach. This single atom tailoring strategy ensures the optimal combination of SA and ECSA to deliver the highest mass activity and durability for diverse electrochemical reactions. In the second part of the dissertation, we will introduce the direct synthesis of single-atom Rh tailored Pt nanowires (SARh-PtNWs) with optimum surface oxophilicity for the hydrogen oxidation reaction. The optimal surface oxophilicity on the SARh Pt nanowires surface ensures the optimum OHads/H2O↓ adsorption on the single-atom Rh sites at 0 V vs. RHE, which facilitates the removal of Hads and hence accelerates the total hydrogen oxidation rate by over one magnitude compared to that of Pt. Apart from the single-atom tailoring strategy, in the third part, we will discuss a unique surface decoration of the Pt-tetrapod framework with water-permeable amorphous Ni(OH)2 shell. Such decoration will keep the Pt sites covered from accessing the reactant such as water, proton, and hydroxyl, and thus can boost the MA and SA simultaneously

Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction

Source data for plots in main figure