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The stability of electrocatalysts during the hydrogen evolution reaction (HER) is vital for efficient production of hydrogen energy. Herein, we demonstrate that silver nanowire aerogel-based support (AABS) could facilitate the construction of HER catalysts with extraordinary long-term stability. A full nanostructure catalyst of nickel phosphide based formed on AABS (Ni2P–Ni5P4@AABS) was prepared to achieve an overpotential of 687 mV (without iRcompensation) for HER at the current density of 1 A cm–2in 0.5 M H2SO4. Excitingly, the stable HER performance was kept for 42 days during the long-term stability (i–t) test at high current density (0.5–1 A cm–2). The excellent HER performance of the Ni2P–Ni5P4@AABS catalyst is attributed to rapid electron transport pathways, numerous more accessible active sites, and support induced enhanced catalytic activity. The support effect was highlighted by a proposed phenomenological two-channel model for electron transport, which provides fresh insights into the design strategy for energy storage and delivery.

Fully understanding of multistate quantum systems could become formidable if not impossible as the system dimensionality increases. One ideal strategy to comprehend complex systems is to transform the system representation into a more structural one so that major characteristics, connections, and even underlying mechanisms can stand out from the huge unstructured information, e.g., the construction of spin eigenfunctions for a system of multiple spins through the diagonalization of the system Hamiltonian matrix. Here, instead of direct matrix diagonalization, the recently developed modular tensor diagram approach is applied to reorganize the state space structure of multispin systems, extending previous investigations on exciton pair states to exciton trimer states. This implementation demonstrates that the proposed approach not only provides a systematical way to transform the high dimensional multistate system into a well organized structure based on basic (exciton) modules but also paves the way to further analysis on potential applications. For example, the analysis on the state space of the exciton trimer system suggests a possible scheme to improve the laser performance via single fission involving multiexcitations and/or multiple fission steps.

Mapping out the high-dimensional state space would be valuable for better understanding the multistate quantum systems. Here, we demonstrate that high-dimensional spin state space can be mapped onto a tensor diagram in full dimension or self-similarly onto the reduced base state space. Based on the tensor diagram, a modular approach is proposed to construct spin eigenfunctions taking the basis of the lower-dimensional space as modules. The implementation of the approach on exciton pair states results in 16 spin eigenstates including 2 singlet states, 3 triplet states, and 1 quintet state with proper symmetry, in contrast to the ones generated using the conventional branching diagram method. The corresponding state energies obtained show the order of spin eigenstates reverses with respect to spin multiplicity. Interestingly, the state space can be decomposed into three subspaces corresponding to the singlet–singlet pair, singlet–triplet pair, and triplet–triplet pair, resulting in a modular structure that is invariant as intermolecular interactions diminish. The proposed approach offers a new perspective on the state space structure of multiple spin states, featuring a hierarchical symmetry, which could be extended to general high-dimensional quantum multistate systems.

Both quantum coherent and incoherent mechanisms have been revealed in singlet exciton fission. Also, in some systems, both mechanisms may concurrently operate. However, the comprehensive picture is not fully understood yet. Here, we proposed a theoretical model for quantum transition (QT) from the coherent to incoherent regime in singlet fission (SF) featuring a characteristic factor of the ratio between the fluctuation of the electron–phonon coupling energy and the effective interstate couplings, in connection with the theory of Anderson localization. The model is demonstrated to be able to interpret the nonadiabatic molecular dynamics simulation of SF in quantitative details, providing an intuitive mechanical picture on how the QT takes place and how the coherent and incoherent components of the fission dynamic could coexist, which would be valuable for understanding fission mechanisms and developing new fission materials.

The recently developed multistate trajectory approach is implemented for nonadiabatic molecular dynamics simulations on electron-coupled Li ion diffusion in LiFePO4, a promising cathode material for lithium ion batteries. The approach is demonstrated to be highly efficient and numerically stable in treating realistic complex molecular systems including tens of electronic states and hundreds of particles and to be capable of providing inspiring molecular pictures via a multistate representation on nonadiabatic quantum dynamics, such as Li ion diffusion and its correlation with electron transport in LiFePO4. The results from our real time nonequilibrium simulations indicate that the electron-coupled Li ion diffusion is significantly enhanced upon the formation of a small polaron, and nonadiabatic couplings further facilitate Li ion diffusion. Therefore, we suggest that nonequilibrium diffusion and nonadiabatic couplings could also be responsible for the wide range of Li ion diffusion coefficients obtained from various theoretical calculations and experimental measurements. Our findings may aid in the understanding of the molecular mechanisms of Li ion diffusion in LiFePO4and design of new cathode materials for lithium ion batteries.

Hydrogen adsorption on interfaces plays an indispensable role in catalytic processes such as the hydrogen evolution reaction. Despite extensive studies, the underlying mechanism of interfacial adsorption is not fully understood. Here, we performed the DFT calculations on the hydrogen adsorption on the metal surface near the Ni/NiO interface. The results reveal that the hydrogen adsorption is site-dependent, and the interfacial effect exhibits a strong dependence on the distance to the boundary. The electronic structure analysis suggests that both the ligand effect and charge transfer effect contribute to weakening the hydrogen adsorption near the Ni/NiO boundary. The incorporation of the d-band center shift and the oxidation state of the adsorption site as the effective descriptor is suggested to understand the underlying mechanism of surface adsorption. The descriptor seems to capture the structural sensitivity in hydrogen adsorption across a variety of interfacial models fairly well, and a nearly linear relationship is found between ΔGHand the descriptor.

Nonadiabatic relaxation of one singlet state into two triplet states is the key step in singlet fission dynamics, the understandings of which may help design next generation solar cells. In this work we perform the symmetrical quasi-classical (SQC) nonadiabatic molecular dynamics (MD) simulation [Cotton and Miller, J. Phys. Chem. A, 2013, 117, 7190; Meyer and Miller, J. Chem. Phys.1979, 70, 3214] for a model system to study the real-time fission dynamics. The dependence of the nonadiabatic relaxation dynamics on energy levels, electronic couplings, and electronic-phonon couplings has been examined, in comparison with other analytical approximations, such as Förster theory and Marcus theory. Unlike many other methods, the SQC nondiabatic MD simulation approach is able to describe fission dynamics efficiently and accurately enough to provide microscopic insights into singlet fission.

Interactions between electronic states and the environmental phonon bath in singlet fission plays a vital role in understanding the underlying mechanisms. In this work we apply the symmetrical quasiclassical nonadiabatic molecular dynamics simulation method [Cotton, S. J.; Miller, W. H. J. Phys. Chem. A2013, 117, 7190 and Meyer, H. D.; Miller, W. H. J. Chem. Phys.1979, 70, 3214] to a model system of singlet fission materials and examine the dependence of fission dynamics on some key factors in the bath modeling, such as, functional form of spectra density, characteristic frequencies, reorganization energy, and bath temperatures. Possible schemes of engineering the phonon spectrum to control fission dynamics have been discussed.

The recently developed symmetrical quasi-classical (SQC) method (Cotton, S. J.; Miller, W. H. J. Phys. Chem. A,2013, 117, 7190) has been applied to a model system for molecular dimers of polyacenes, a family of organic materials for highly efficient solar energy conversion by using singlet fission (SF). Our results describe the electronic–nuclear coupled dynamics of singlet fission very well for the model system, in good agreement with those recently obtained by using Redfield theory. The quantum interference between the charge transfer mediated pathway and the direct pathway of singlet fission has been investigated, and we found that pathway coherence may change the short-time SF dynamics quite a lot, even though the direct pathway itself may be very slow. The SQC method performs very efficiently in treating the model system with up to several thousand degrees of freedom and therefore shows a potential to be implemented to real complex molecular systems, such as singlet fission materials.