Machine learning-guided synthesis of advanced inorganic materials

Synthesis of advanced inorganic materials with minimum number of trials is of paramount importance towards the acceleration of inorganic materials development. The enormous complexity involved in existing multi-variable synthesis methods leads to high uncertainty, numerous trials and exorbitant cost. Recently, machine learning (ML) has demonstrated tremendous potential for material research. Here, we report the application of ML to optimize and accelerate material synthesis process in two representative multi-variable systems. A classification ML model on chemical vapor deposition-grown MoS2 is established, capable of optimizing the synthesis conditions to achieve higher success rate. While a regression model is constructed on the hydrothermal-synthesized carbon quantum dots, to enhance the process-related properties such as the photoluminescence quantum yield. Progressive adaptive model is further developed, aiming to involve ML at the beginning stage of new material synthesis. Optimization of the experimental outcome with minimized number of trials can be achieved with the effective feedback loops. This work serves as proof of concept revealing the feasibility and remarkable capability of ML to facilitate the synthesis of inorganic materials, and opens up a new window for accelerating material development

Engineering grain boundaries at the 2D limit for the hydrogen evolution reaction

Atom-thin transition metal dichalcogenides (TMDs) have emerged as fascinating materials and key structures for electrocatalysis. So far, their edges, dopant heteroatoms and defects have been intensively explored as active sites for the hydrogen evolution reaction (HER) to split water. However, grain boundaries (GBs), a key type of defects in TMDs, have been overlooked due to their low density and large structural variations. Here, we demonstrate the synthesis of wafer-size atom-thin TMD films with an ultra-high-density of GBs, up to ~1012 cm−2. We propose a climb and drive 0D/2D interaction to explain the underlying growth mechanism. The electrocatalytic activity of the nanograin film is comprehensively examined by micro-electrochemical measurements, showing an excellent hydrogen-evolution performance (onset potential: −25 mV and Tafel slope: 54 mV dec−1), thus indicating an intrinsically high activation of the TMD GBs

Tunable metal contacts at layered black-arsenic/metal interface forming during metal deposition for device fabrication

Understanding the kinetics of interfacial reaction in the deposition of metal contacts on 2D materials is important for determining the level of contact tenability and the nature of the contact itself. Here, we find that some metals, when deposited onto layered black-arsenic films using e-beam evaporation, form a-few-nm thick distinct intermetallic layer and significantly change the nature of the metal contact. In the case of nickel, the intermetallic layer is Ni11As8, whereas in the cases of chromium and titanium they are CrAs and a-Ti3As, respectively, with their unique structural and electronic properties. We also find that temperature, which affects interatomic diffusion and interfacial reaction kinetics, can be used to control the thickness and crystallinity of the interfacial layer. In the field effect transistors with black-arsenic channel, due to the specifics of its formation, this interfacial layer introduces a second and more efficient edge-type charge transfer pathway from the metal into the black-arsenic. Such tunable interfacial metal contacts could provide new pathways for engineering highly efficient devices and device architectures

Self-gating in semiconductor electrocatalysis

The semiconductor-electrolyte interface dominates the behaviours of semiconductor electrocatalysis, which has been modelled as a Schottky-analogue junction according to classical electron transfer theories. However, this model cannot be used to explain the extremely high carrier accumulations in ultrathin semiconductor catalysis observed in our work. Inspired by the recently developed ion-controlled electronics, we revisit the semiconductor-electrolyte interface and unravel a universal self-gating phenomenon through microcell-based in situ electronic/electrochemical measurements to clarify the electronic-conduction modulation of semiconductors during the electrocatalytic reaction. We then demonstrate that the type of semiconductor catalyst strongly correlates with their electrocatalysis; that is, n-type semiconductor catalysts favour cathodic reactions such as the hydrogen evolution reaction, p-type ones prefer anodic reactions such as the oxygen evolution reaction and bipolar ones tend to perform both anodic and cathodic reactions. Our study provides new insight into the electronic origin of the semiconductor-electrolyte interface during electrocatalysis, paving the way for designing high-performance semiconductor catalysts.NRF (Natl Research Foundation, S’pore)ASTAR (Agency for Sci., Tech. and Research, S’pore)MOE (Min. of Education, S’pore)Accepted versio

Amorphizing noble metal chalcogenide catalysts at the single-layer limit towards hydrogen production

Rational design of noble metal catalysts with the potential to leverage efficiency is vital for industrial applications. Such an ultimate atom-utilization efficiency can be achieved when all noble metal atoms exclusively contribute to catalysis. Here, we demonstrate the fabrication of a wafer-size amorphous PtSex film on a SiO2 substate via a low-temperature amorphization strategy, which offers single-atom-layer Pt catalysts with high atom-utilization efficiency (~26 wt%). This amorphous PtSex (1.2 < x < 1.3) behaves as a fully activated surface, accessible to catalytic reactions, and features a nearly 100% current density relative to a pure Pt surface and reliable production of sustained high-flux hydrogen over a 2 inch wafer as a proof-of-concept. Furthermore, an electrolyser is demonstrated to generate a high current density of 1,000 mA cm−2. Such an amorphization strategy is potentially extendable to other noble metals, including the Pd, Ir, Os, Rh and Ru elements, demonstrating the universality of single-atom-layer catalysts