Solar-Driven Water Splitting at 13.8% Solar-to-Hydrogen Efficiency by an Earth-Abundant Electrolyzer

Joakim Ekspong,Christian Larsen,Wai Ling Kwong,Johannes Messinger,Thomas Wågberg,Jinbao Zhang,Jia Wang,Jonas Stenberg,Erik M J Johansson,Ludvig Edman

doi:10.1021/acssuschemeng.1c03565

Joakim Ekspong, Christian Larsen + Show 8 more

Open Access

https://doi.org/10.1021/acssuschemeng.1c03565

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Abstract

We present the synthesis and characterization of an efficient and low cost solar-driven electrolyzer consisting of Earth-abundant materials. The trimetallic NiFeMo electrocatalyst takes the shape of nanometer-sized flakes anchored to a fully carbon-based current collector comprising a nitrogen-doped carbon nanotube network, which in turn is grown on a carbon fiber paper support. This catalyst electrode contains solely Earth-abundant materials, and the carbon fiber support renders it effective despite a low metal content. Notably, a bifunctional catalyst–electrode pair exhibits a low total overpotential of 450 mV to drive a full water-splitting reaction at a current density of 10 mA cm–2 and a measured hydrogen Faradaic efficiency of ∼100%. We combine the catalyst–electrode pair with solution-processed perovskite solar cells to form a lightweight solar-driven water-splitting device with a high peak solar-to-fuel conversion efficiency of 13.8%.

Highlights

The ever-increasing energy demand, spurred by an overall global increase in living standards and a larger world population estimated to reach 10 billion people in 2060, in combination with global warming, mandates a fast transition to renewable energy sources.[1]
Transition metal oxides, based on Ni, Fe, and Co, have been shown to exhibit low overpotential for the oxygen evolution reaction (OER), in line with the best noble metal oxides RuO2 and IrO2, but few examples of such catalysts are reported for the hydrogen evolution reaction (HER),[11] approaches such as vacancy engineering,[12−15] bimetallic alloying, and addition of phosphides[12,16] have shown to be promising strategies to lower the overpotential for metals toward HER in alkaline conditions.[17,18]
An essential aspect for a well-coated catalyst structure is the high number of adhesion sites on the nitrogen-functionalized carbon nanotubes, which previously has been proven to be beneficial for catalysts anchoring.[20−22] it has been shown that the introduced nitrogen defects in the NCNTs result in an increased electrical conductivity compared to pristine CNTs.[34]

Summary

■ INTRODUCTION

The ever-increasing energy demand, spurred by an overall global increase in living standards and a larger world population estimated to reach 10 billion people in 2060, in combination with global warming, mandates a fast transition to renewable energy sources.[1]. Transition metal oxides, based on Ni, Fe, and Co, have been shown to exhibit low overpotential for the oxygen evolution reaction (OER), in line with the best noble metal oxides RuO2 and IrO2, but few examples of such catalysts are reported for the hydrogen evolution reaction (HER),[11] approaches such as vacancy engineering,[12−15] bimetallic alloying, and addition of phosphides[12,16] have shown to be promising strategies to lower the overpotential for metals toward HER in alkaline conditions.[17,18] In recent years, the best catalyst electrodes are usually supported on Received: June 2, 2021 Revised: September 23, 2021 Published: October 13, 2021. The low overall overpotential allows us to operate our complete water-splitting device, comprising our hybrid catalyst electrodes and two serially connected solution-processed perovskite solar cells, with a high solar-to-hydrogen conversion efficiency (STH) of 13.8%

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES