Toward a Low‐Cost Artificial Leaf: Driving Carbon‐Based and Bifunctional Catalyst Electrodes with Solution‐Processed Perovskite Photovoltaics

Abstract

countries, where many users still are not connected to the electric grid, it is clear that alternative energy technologies are needed that can contribute with renewable fuels in signifi cant amounts. In this challenging context, researchers have found inspiration in the process of natural photosynthesis when they attempt to convert the plentiful, but intermittent, solar irradiation incident on the Earth's surface into a storable fuel, using a range of methods commonly coined as artifi cial photosynthesis. [1][2][3][4][5][6][7][8][9] One emerging technology to achieve such solar-to-fuel conversion is the "artifi cial-leaf device", which essentially comprises an assembly of photovoltaics (PVs) that drives two electrocatalyst electrodes immersed in water. [10][11][12] This device produces molecular hydrogen and oxygen using only sunlight and water as the input, and during the past few years its performance has improved drastically, with the current record for the solar-to-hydrogen (STH) conversion efficiency being above 10%. [13][14][15][16] It is, however, clear that in order to become truly sustainable and useful, the artifi cial-leaf device should comprise solely, or predominantly, earth-abundant materials and be produced with scalable and low-cost methods. Moreover, from a processing and transport point of view, it is preferable if it can be lightweight and fl exible.Perovskite materials [ 14,[17][18][19][20][21] have recently emerged as an interesting option to incumbent silicon [ 15,20 ] and copperindium-gallium-selenide [ 16,20 ] for the active material in PVs, due to a high and quickly improving solar-to-electric (STE) conversion effi ciency and an opportunity for cost-effi cient, solutionbased fabrication. [ 17,18,21,23 ] The electrocatalyst electrode comprises a catalytically active material deposited on the surface of a current collector. Commonly employed materials for the current collector are bulk or porous metals, [ 15 ] whereas a popular choice for the catalyst is various types of metal-oxides. [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] From a system-cost and practicality perspective, it is desirable to develop a functional lightweight and low-cost current collector and to identify a catalyst that is bifunctional in that it can drive the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in the same water solution. [ 14,[39][40][41][42][43][44] Here, we present an artifi cial-leaf device that delivers an STH effi ciency of 6.2% and a Faradaic H 2 evolution effi ciency of 100%. We mention that our device is not fully integrated at this stage, Molecular hydrogen can be generated renewably by water splitting with an "artifi cial-leaf device", which essentially comprises two electrocatalyst electrodes immersed in water and powered by photovoltaics. Ideally, this device should operate effi ciently and be fabricated with cost-effi cient means using earth-abundant materials. Here, a lightweight electrocatalyst electrode, comprising large surface-area NiCo 2 O 4 nano...

Towards High‐Performance Aqueous Sodium‐Ion Batteries: Stabilizing the Solid/Liquid Interface for NASICON‐Type Na2VTi(PO4)3 using Concentrated Electrolytes

“…All cellse xhibit ac urrent peak at V % 1.2 Vc orresponding to the potential difference between the V 3 + /V 4 + and Ti 4 + /Ti 3 + redox couples in NVTP/C.T he peak intensities decrease upon increasing the concentration of the NaClO 4 salt;h owever,t he lowest peak separation is observed with the 8 m NaClO 4 electrolyte, which indicates that, despite the lower conductivity,i ncreased ion aggregation facilitates charge transfer at the electrode surface. [34,45] The first charge capacity of all cells is close to the theoreticalv alue (i.e.,6 2mAh g À1 ). Notably,t he influence of the current collector (carbon paper or stainless steel) was also studied because of the few studies available (see Figure S4).…”

“…[44] Given that hydrogen evolution and poor performance were observed with carbon paper,a ll experiments were performed by using stainless-steel current collectors. [34,45] The first charge capacity of all cells is close to the theoreticalv alue (i.e.,6 2mAh g À1 ). However,d uring the first discharge am uch lower capacity is detected, which results in al ow initial coulombic efficiency,i na ccordancew ith other studies on aqueous Li-a nd Na-ion batter-ies.…”

Electrocatalytic Water Oxidation by MnOx/C: In Situ Catalyst Formation, Carbon Substrate Variations, and Direct O2/CO2 Monitoring by Membrane‐Inlet Mass Spectrometry

“…[41][42][43] Recently,t he direct carbonization of porphyrin or corrolec omplexeso ft he respective metals at high temperatures hasg ained much attraction as ap romising method to directly prepare electrode materials. [44][45][46] However, only as mall number of studies concerning anodes prepared from manganese oxidesa nd carbon materials have been reported.…”

“…OER catalysis using earth-abundant transition metals (especially Ni, [35,36] Fe, [37,38] Co, [39,40] and Mn) oxides is currently being intensely studied and carbon support materials have also been used in this context. [41][42][43] Recently,t he direct carbonization of porphyrin or corrolec omplexeso ft he respective metals at high temperatures hasg ained much attraction as ap romising method to directly prepare electrode materials. [44][45][46] However, only as mall number of studies concerning anodes prepared from manganese oxidesa nd carbon materials have been reported.…”

Macroscopic‐Scale Three‐Dimensional Carbon Nanofiber Architectures for Electrochemical Energy Storage Devices

“…[158] Carbon papers are also employed as the template to grow different kinds of materials and construct 3D CNF architectures. For example, vertical α-FeOOH nanowires [159] and TiO 2 [160] are successfully grown on the surface of carbon paper in a low-temperature hydrothermal procedure; porous and polycrystalline NiCo 2 O 4 nanorods entangled with and attached to a nitrogen-doped carbon nanotubes (N-CNTs) network are anchored onto carbon paper in a CVD process; [161] MoS 2 nanosheets are also grown on carbon fiber paper via CVD technology [162] and hydrothermal method; [163] 3D CNTs and borondoped carbon nanorods are directly grown on carbon papers by spray pyrolysis and CVD method; [164] CoSe 2 nanoparticles are grown on the surface of carbon paper by preparing Co 3 O 4 nano particles on carbon microfiber paper followed by selenization under Se vapor. [165] In addition, macroporous carbon fiber felt, consisting of an interwoven matrix of thermally conductive carbon fibers with a diameter of approximately 10-20 mm, is used as the template to fabricate 3D CNFs nanostructures.…”