Mixing Entropy Battery Extracts Energy from Salinity Difference
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Solution Overview
Problem
Existing technologies fail to efficiently harness the renewable energy generated by the salinity difference between seawater and freshwater, with low energy efficiencies and high costs limiting large-scale utilization.
Innovation Solution
A mixing entropy battery system that extracts energy from the salinity difference by using selective electrodes to store and release ions, overcoming challenges of self-discharge and low energy densities, with an energy extraction efficiency of up to 85%.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If membrane-based techniques (pressure-retarded osmosis, reverse electrodialysis) are used to extract energy from salinity difference, then energy extraction is enabled, but energy efficiency is low and costs are high due to membrane fouling and high internal resistances
Solution Approach 1:
The patent removes membranes from the energy extraction system entirely. Instead of using membrane-based techniques (pressure-retarded osmosis, reverse electrodialysis), the invention employs a battery system with selective electrodes that directly convert salinity difference into electrical energy through electrochemical reactions, eliminating membrane fouling and associated efficiency losses
Solution Approach 2:
The patent replaces the mechanical/membrane-based energy extraction process with an electrochemical battery system. The selective electrodes (anion-exchange and cation-exchange electrodes) create electrochemical potential differences that drive electron flow, substituting the mechanical pressure-driven processes with electrochemical energy conversion
2Loss of energy
If concentration electrochemical cells are used to capture energy from chloride ion concentration difference, then energy extraction is achieved, but at least half of available energy is lost since free energy is stored nearly equally by both anions and cations
Solution Approach 1:
The patent applies different electrode materials with specific ion-selective properties at different locations in the battery. The anion-exchange electrode selectively interacts with anions while the cation-exchange electrode selectively interacts with cations, allowing the system to capture energy from both ion types simultaneously rather than limiting to one ion species
Solution Approach 2:
The battery system is designed to handle multiple ion types (both cations and anions) through complementary electrode pairs. This multi-functional approach allows the system to extract energy from the complete salinity difference rather than relying on a single ion type, doubling the potential energy capture
3Loss of energy
If supercapacitor electrodes are used for energy extraction from salinity difference, then energy extraction is enabled, but energy conversion efficiency is limited to less than 24% due to self-discharge and surface-limited charge storage
Solution Approach 1:
The patent uses stable, long-lasting battery electrodes instead of fragile supercapacitor electrodes. The electrochemical battery system provides sustained energy extraction over extended periods without the self-discharge issues that plague supercapacitor-based systems, offering greater operational reliability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The mixing entropy battery achieves significantly higher energy extraction efficiency compared to previous technologies, potentially generating 2 TW of renewable energy, approximately 13% of current global energy consumption, while minimizing environmental impact.
Implementation Method 1
A mixing entropy battery system that extracts energy from the salinity difference by using selective electrodes to store and release ions
Implementation Method 2
The entropic energy created by the difference in water salinities is normally dissipated when river water flows into the sea. This reduction in free energy due to the mixing is estimated at about 2.2 kJ of free energy per liter of fresh water that flows into the sea (based on the osmotic pressure difference between fresh water and sea water)
Implementation Method 3
Energy is extracted from a difference in concentration of the ions between two electrolytes
Data Source
AI summary
An electrochemical system includes: (1) a battery including an anode and a cathode; (2) a first source of a first electrolyte having a first concentration of ions; (3) a second source of a second electrolyte having a second concentration of the ions, wherein the second concentration is greater than the first concentration; and (4) a fluid conveyance mechanism connected between the battery and each of the first source and the second source. During charging of the battery, the anode and the cathode are at least partially immersed in the first electrolyte, and, during discharging of the battery, the anode and the cathode are at least partially immersed in the second electrolyte. The fluid conveyance mechanism exchanges the first electrolyte with the second electrolyte between charging and discharging of the battery, and exchanges the second electrolyte with the first electrolyte between discharging and charging of the battery.