Search

Photoelectrochemical water splitting is one of the sustainable routes to renewable hydrogen production. One of the challenges to deploying photoelectrochemical (PEC) based electrolyzers is the difficulty in the effective capture of solar radiation as the illumination angle changes throughout the day. Herein, we demonstrate a method for the angle-independent capture of solar irradiation by using transparent 3 dimensional (3D) lattice structures as the photoanode in PEC water splitting. The transparent 3D lattice structures were fabricated by 3D printing a silica sol–gel followed by aging and sintering. These transparent 3D lattice structures were coated with a conductive indium tin oxide (ITO) thin film and a Mo-doped BiVO4 photoanode thin film by dip coating. The sheet resistance of the conductive lattice structures can reach as low as 340 Ohms per sq for ∼82% optical transmission. The 3D lattice structures furnished large volumetric current densities of 1.39 mA cm−3 which is about 2.4 times higher than a flat glass substrate (0.58 mA cm−3) at 1.23 V and 1.5 G illumination. Further, the 3D lattice structures showed no significant loss in performance due to a change in the angle of illumination, whereas the performance of the flat glass substrate was significantly affected. This work opens a new paradigm for more effective capture of solar radiation that will increase the solar to energy conversion efficiency. Ministry of Education (MOE) National Research Foundation (NRF) Published version This work was supported by the Singapore Ministry of Education (MOE) Tier 2 grant (MOE T2EP50120-00081) and Tier 1 grant (2020-T1-001-147 (RG64/20)). This research was also supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Campus of Research Excellence and Technological Enterprise (CREATE) programme

Synthesis and coating of multi-metal oxides (MMOs) and alloys on conductive substrates are indispensable to electrochemical applications, yet demand multiple, resource-intensive, and time-consuming processes. Herein, an alternative approach to the synthesis and coating of alloys and MMOs by femtosecond laser direct writing (FsLDW) is reported. A solution-based precursor ink is deposited and dried on the substrate and illuminated by a femtosecond laser. During the illumination, dried precursor ink is transformed to MMO/alloys and is simultaneously bonded to the substrate. The formulation of the alloy and MMO precursor ink for laser processing is universally applicable to a large family of oxides and alloys. The process is conducted at room temperature and in an open atmosphere. To demonstrate, a large family of 57 MMOs and alloys are synthesized from a group of 13 elements. As a proof of concept, Ni0.24 Co0.23 Cu0.24 Fe0.15 Cr0.14 high entropy alloy synthesized on stainless-steel foil by FsLDW is used for the oxygen evolution reaction, which achieves a current density of 10 mA cm-2 at a significantly low overpotential of 213 mV. Further, FsLDW can also achieve microfabrication of alloys/MMO with feature sizes down to 20 µm. The authors acknowledge funding received from the research collaboration agreement by Panasonic Factory Solutions Asia Pacific Pte. Ltd. (PFSAP) and Singapore Centre for 3D Printing (RCA-15/027). This work was also partially supported by the National Research Foundation of the Republic of Korea (NRF-2012R1A3A1050386 and NRF-2021R1A4A1031660), the Basic Research Program (NK224C) funded by the Korea Institute of Machinery and Materials (KIMM), and by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, and Forestry (IPET) funded by the Ministry of Agriculture, Food and Rural Affairs (MAFRA) (321077-2).

The necessity of Earth-abundant low-cost catalysts with activity similar to noble metals such as platinum is indispensable in order to realize the production of hydrogen through electrolysis of water. Herein, we report a relatively low-cost NiAg0.4 3D porous nanocluster catalyst whose activity matches with that of the state-of-the-art Pt/C in 1 M KOH solution. The catalyst is designed on the principle of creating an interface between a metal having a positive Gibbs energy of hydrogen adsorption and a metal of negative Gibbs energy based on the volcano plot, to tune the Gibbs energy of hydrogen adsorption near zero for enhanced hydrogen evolution. The synthesized NiAg0.4 3D porous nanoclusters are comprised of nanoparticles of lateral dimension ∼50 nm forming a 3D porous network with pores of 10 nm–80 nm. A high-resolution transmission electron microscopy image reveals the epitaxial growth of Ag (200) on the Ni (111) plane leading to the creation of abundant interfaces between the Ni and Ag lattices. The catalyst needs a low overpotential of 40 mV@10 mA cm−2 with a Tafel slope of 39.1 mV dec−1 in 1 M KOH solution. Furthermore, the catalyst exhibits a high specific activity of 0.1 mA cm−2(ECSA) at an overpotential (η) of 45 mV which matches with the specific activity of Pt/C 20% wt. catalyst (0.1 mA cm−2@η = 26 mV). Density functional theory calculations reveal that the Ni–Ag interface furnishes a pathway with a reduced Gibbs energy of adsorption of −0.04 eV, thus promoting enhanced hydrogen evolution. In summary, this study reveals excellent HER activity at the Ni–Ag interface.

Highly active catalysts from the earth-abundant metals are essential to materialize the low-cost production of hydrogen through water splitting. Herein, nickel porous networks codoped with Cu and Fe prepared by thermal reduction of presynthesized Cu, Fe-codoped Ni(OH)2 nanowires are reported. The sample consists of nanoparticles of ∼80 nm, which form highly porous network clusters of ∼1 μm with a pore size of 10–100 nm. Among the various doped compositions, the NiCu0.05Fe0.025 porous network exhibits the best catalytic activity with a low overpotential of 60 mV for a hydrogen evolution reaction (HER) in 1 M KOH solution and a specific activity of 0.1 mA cm–2 at 117 mV overpotential calculated based on the electrochemical active surface area (ECSA). The density functional theory calculations reveal that codoping of Fe and Cu into the Ni lattice results in a shift of d-bands of nickel to lower energy levels and thus in the reduced hydrogen adsorption energy (ΔGH = −0.131 eV), which is close to ΔGH for Pt (−0.09 eV). When NiCu0.05Fe0.025(OH)2 nanowires is used as an oxygen evolution reaction (OER) catalyst and is coupled with NiCu0.05Fe0.025 porous networks for overall water splitting, the NiCu0.05Fe0.025∥NiCu0.05Fe0.025(OH)2 catalyst couple achieves a current density of 10 mA cm–2 at 1.491 V, similar to that of the Pt/C∥RuO2 couple and offers a negligible loss in the performance when operated at 20 mA cm–2 for 30 h. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

The necessity of Earth-abundant low-cost catalysts with activity similar to noble metals such as platinum is indispensable in order to realize the production of hydrogen through electrolysis of water. Herein, we report a relatively low-cost NiAg

Porous graphene (PG) devices fabricated in situ from polyimide (PI) adhered onto paper substrates provide a cost-effective and recycling-friendly alternative to re-engineer paper for liquid-based power sources and sensors. However, paper is generally damaged due to heating during the fabrication of PG devices. Here integrated graphene-paper electronics with exceptional thermal control through the proposed thermally localized laser graphitization (LLG) process is demonstrated, employing optimized ultrafast laser writing. LLG enables in situ fabrication of localized porous graphene (LPG) devices (>1775 K) on 65 µm thick PI tape adhered to paper without heating above 348 K. Laser parameters for LLG are predicted using an analytical temperature model and validated experimentally. The LLG is demonstrated by fabricating liquid electrolyte LPG micro-supercapacitors and humidity sensors on liquid susceptible paper. It is envisaged that the scientific concepts proposed and demonstrated here will expedite the development of low-cost, scalable, and chemically robust LPG devices on thermally sensitive substrates. Ministry of Education (MOE) Funding: This work is supported under the research collaboration agreement by Panasonic Factory Solutions Asia Pacific (PFSAP) and Singapore Centre for 3D Printing (SC3DP) (RCA-15/027). V.M.M. also acknowledges the financial support received through COLE-EDB, and MOE Tier 1 Grant RG192/17. S.W.L. acknowledges the support by Academic Research Fund Tier 2 from Ministry of Education, Singapore under ref. no. 2018-T2-1-045.

With an increasing energy consumption rate and rising global population, constructing sustainable energy technologies has become one of the major scientific challenges. Therefore, the development of electrocatalytic conversion technologies that can convert renewable resources, such as water and nitrogen, into value-added chemicals or fuels (e.g., hydrogen and ammonia) can be crucial. A number of transition metal carbides (TMCs) have been investigated over the past few years as effective electrocatalysts for various reactions. This is mainly owing to their unique electronic structures, which leads to high electrical conductivity and chemical stability. Moreover, the reactivity of TMC-based electrocatalysts is highly dependent on their surface and interfacial properties. This review focuses on tuning nanostructures and interfaces to enhance the electrocatalytic activity of TMC-based materials for hydrogen production and nitrogen fixation. The mechanisms behind the surface and interface engineering are discussed, including the synergy effects, facet binding energy, active defects, and low-coordinated sites. In particular, studies on activity enhancement through design of the interfacial phase, composition, and structure in TMC-based electrocatalysts are highlighted. The effective tuning strategies might pave the way for future development of highly active TMC-based electrocatalysts for sustainable energy-related conversion. MOE (Min. of Education, S’pore) Accepted version